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STATE  OF  ILLINOIS 

DEPARTMENT  OF  REGISTRATION  AND  EDUCATION 

A.  M.  SHELTON,  Director 

% 

DIVISION  OF  THE 

STATE  GEOLOGICAL  SURVEY 

M.  M.  LEIGHTON.  Chief 


REPORT  OF  INVESTIGATIONS— NO.  13 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF 

NORTHERN  ILLINOIS 

WITH  SPECIAL  REFERENCE  TO  UNDERGROUND 

WATER  SUPPLIES 


PRINTED  BY  AUTHORITY  OF  THE  STATE  OF  ILLINOIS 


URBANA,  ILLINOIS 
1927 


ILLINOIS  STATE  LIBRARY 


STATE  OF  ILLINOIS 

DEPARTMENT  OF  REGISTRATION  AND  EDUCATION 

A.  M.  SHELTON.  Director 

DIVISION  OF  THE 

STATE  GEOLOGICAL  SURVEY 

M.  M.  LEIGHTON.  Chief 


Committee  of  the  Board  of  Natural  Resources 

and  Conservation 

A.  M.  Sheltox,  Chairman 

Director  of  Registration  and  Education 

Charles  M.  Thompson' 

Representing  the  President  of  the  Uni¬ 
versity  of  Illinois 

Epson  S.  Rastin 
Geologist 


—  •uta  [COUNCIL  * 


Jeffersons  Printing  &  Stationery  Co. 
Springfield,  Illinois 
1927 


The  accompanying  report  on  Stratigraphy  and  Geologic  Structure 
of  Northern  Illinois  with  Special  Reference  to  Underground  Water 
Supplies  has  been  in  the  process  of  preparation  for  some  time.  Most  of 
the  buried  rock  formations  of  northern  Illinois  have  been  studied  in 
surface  exposures  in  Wisconsin  by  the  author,  Mr.  F.  T.  Thwaites  of 
the  Wisconsin  Geological  and  Natural  History  Survey,  and  the  Illinois 
State  Geological  Survey  has  been  fortunate  in  securing  his  interest  in 
the  study  of  the  well  cuttings  of  a  large  number  of  wells  in  that  part 
of  the  State.  Mr.  Thwaites  has  also  given  much  attention  to  the  ap¬ 
plication  of  geologic  knowledge  to  well  drilling  for  water  recovery.  It 
is  therefore  believed  that  this  report  will  be  helpful  to  those  seeking 
information  regarding  the  geologic  conditions  of  northern  Illinois  from 
the  standpoint  of  underground  water  supplies. 

The  report  has  had  the  benefit  of  a  careful  review  by  Mr.  G.  C. 
Habermeyer,  Engineer  of  the  Illinois  State  Water  Survey,  which  both 
the  author  and  the  Illinois  State  Geological  Survey  gratefully  ac¬ 
knowledge. 

M.  M.  Leighton,  Chief, 
State  Geological  Survey  Division. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE 

OF  NORTHERN  ILLINOIS 

WITH  SPECIAL  REFERENCE  TO  UNDERGROUND  WATER  SUPPLIES 

By  F.  T.  Thwaites 

OUTLINE 

Page 


Introduction  .  9 

Geologic  formations  and  their  water  supplies .  9 

General  statement  .  9 

Pennsylvanian  system  .  10 

McLeansboro,  Carbondale,  and  Pottsville  formations .  10 

Description  .  10 

Water  supplies  .  11 

Drilling  conditions  .  11 

Devonian  system  .  11 

Sweetland  Creek  shale,  Cedar  Valley  limestone,  and  Wapsipinicon 

limestone  .  11 

Silurian  system  .  12 

Niagaran  dolomite,  Kankakee  limestone,  and  Edgewood  formation 

(Niagaran  and  Alexandrian  series) .  12 

Description  . 12 

Water  supplies  .  14 

Drilling  conditions  .  14 

Ordovician  system  .  15 

Maquoketa  shale  (Richmond  group) .  15 

Description  .  15 

Drilling  conditions  .  16 

Galena  and  Platteville  formations  (Trenton  and  Black  River  groups)..  16 

Description  .  16 

Water  supplies  .  18 

Drilling  conditions  .  18 

St.  Peter  Sandstone  .  19 

Description  .  19 

Water  supplies  .  20 

Drilling  conditions  .  20 

Shakopee,  “New  Richmond,”  and  Oneota  formations  (Prairie  du  Chien 

group)  .  21 

Description  .  21 

Water  supplies  .  24 

Drilling  conditions .  24 

Cambrian  system  .  24 

Jordan  and  Trempealeau  formations  .  24 

Description  .  24 

Water  supplies  .  25 

Mazomanie  and  Franconia  formations .  25 

Description  .  25 

Correlation  .  27 

Water  supplies  .  28 

Drilling  conditions .  28 


Page 

Dresbach  sandstone  . # .  28 

Description  .  28 

Water  supplies  .  31 

Eau  Claire  formation  .  31 

Description  .  31 

Water  supplies  .  33 

Drilling  conditions  .  34 

Mt.  Simon  sandstone  .  34 

Description  .  34 

Water  supplies  .  35 

Drilling  conditions  .  36 

Structure  .  36 

Introduction  .  36 

Structural  Features  .  37 

Cause  of  deformation  .  43 

Water  quality  and  problems .  43 

General  statement  .  43 

Nature  of  soft  waters .  43 

Method  of  testing  quality  of  water .  44 

Contamination  of  deep  wells .  45 

Well  construction  .  45 

Future  of  underground  waters .  47 

Well  logs  .  48 

ILLUSTRATIONS 

Figure 

1.  Sketch  map  of  aerial  geology  of  northern  Illinois .  8 

2.  Diagrammatic  columnar  section  of  northeastern  Illinois  showing  revised 

correlation  of  strata  .  29 

Plate 

I.  Structure  map  of  northern  Illinois . In  pocket 

II.  Section  from  Clinton,  Iowa,  to  Chicago,  Illinois . In  pocket 

TABLES 

1.  Correlation  table  of  geologic  names  used  in  Illinois  and  adjacent  states....  9 

2.  Generalized  section  of  Pennsylvanian  rocks  of  La  Salle  County .  10 

3.  Well  log  illustrating  character  of  Devonian  rocks .  12 

4.  Well  logs  illustrating  character  of  Silurian  rocks .  12 

5.  Well  logs  illustrating  character  of  the  Maquoketa  shale .  15 

6.  Well  logs  illustrating  character  of  the  Galena  and  Platteville  formations..  17 

7.  Well  logs  illustrating  character  of  the  St.  Peter  sandstone .  19 

8.  Well  logs  illustrating  character  of  the  Prairie  du  Chien  group .  23 

9.  Well  logs  illustrating  character  of  the  Jordan  and  Trempealeau  formations  25 

10.  Well  logs  illustrating  character  of  the  Mazomanie  and  Franconia  formations  26 

11.  Well  logs  illustrating  character  of  the  Dresbach  sandstone .  30 

12.  Well  logs  illustrating  character  of  the  Eau  Claire  formation .  32 

13.  Well  logs  illustrating  character  of  the  Mt.  Simon  formation .  34 

14.  Well  data  used  in  the  construction  of  the  structure  map  (PI.  I) .  38 


8  STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


Scale  1  inch  =  28  miles 

Sketch  map  of  aerial  geology  of  northern  Illinois. 


INTRODUCTION 


Potable  underground  waters  can  be  obtained  in  quantity  through¬ 
out  northern  Illinois.  They  form  an  important  resource  which  is  utilized 
by  many  industries,  cities,  villages,  and  individuals.  Very  few  cities 
of  the  size  of  Chicago  have  as  large  supplies  of  potable  underground 
water.  Rockford  is  the  largest  city  in  Northern  Illinois  to  use  well  water 
for  its  public  supply. 

The  subject  of  underground  waters  in  northern  Illinois  has  been  in¬ 
vestigated  by  a  number  of  geologists  and  engineers.1  The  attention  of 
the  writer  was  drawn  to  the  district  in  connection  with  studies  in  Wis¬ 
consin  and  the  correlation  of  the  deeply  buried  formations  was  an¬ 
nounced  in  1923. 2  To  simplify  forecasting  of  depths  to  the  Cambrian 
sandstones  a  structure  map  was  made  (PI.  I).  The  present  paper  is 
designed  primarily  as  an  aid  to  engineers  and  well  drillers. 

GEOLOGICAL  LORMATIONS  AND  THEIR 
WATER  SUPPLIES 

General  Statement 

North  of  the  41st  parallel  of  latitude  Illinois  is  underlain  beneath 
the  soil  and  loose  surface  material  by  rocks  of  the  Pennsylvanian,  De¬ 
vonian,  Silurian,  and  Ordovician  systems.  (See  fig.  1.)  Cambrian  rocks 
may  underlie  parts  of  the  Rock  River  valley  but  are  elsewhere  concealed 
under  younger  formations.  In  the  far  northwestern  part  of  the  State  the 
mantle  rock  or  “surface”  was  mainly  formed  by  weathering  of  the  bed 
rocks,  in  part  was  deposited  by  the  wind,  and  in  the  valleys  was  laid 
down  by  streams.  In  the  remainder  of  the  district  the  mantle  rock  was 
deposited  by  glaciers  with  associated  streams  and  lakes;  these  deposits 
are  collectively  known  as  “drift”.  The  bed  rocks  alone  are  discussed  in 
this  report.  The  names  of  the  different  formations  are  those  used  in 
1926  by  the  Illinois  State  Geological  Survey.  For  the  convenience 


iStone,  Leander,  The  artesian  wells  of  Chicago:  Chicago  Acad.  Sci.  Bull.  1,  pp.  93- 
102,  1886. 

Rolfe,  C.  W.,  Artesian  water  from  the  drift  in  eastern  Illinois:  Am.  Geologist,  vol.  6, 
pp.  32-35,  1800. 

Mead,  D.  W.,  Notes  on  the  hydrology  of  Illinois  in  relation  to  its  water  supplies:  Illi¬ 
nois  Soc.  Engr.  Rept.,  vol.  8,  pp.  48-68,  1893. 

Mead,  D.  W.,  The  hydro-geology  of  the  upper  Mississippi  Valley  and  of  some  of  the 
adjoining  territory:  Assoc.  Engrs.  Soc.  Jour.,  vol.  13,  pp.  329-396,  1894. 

Leverett,  Frank,  The  water  resources  of  Illinois:  U.  S.  Geol.  Survey  Seventeenth 
Ann.  Rept.,  pt.  2.  pp.  695-828,  1896. 

Shufeldt,  G.  A.,  Jr.,  History  of  the  Chicago  artesian  well,  Chicago,  1865,  Religio-Phil- 
osophical  Publishing  Assoc.,  Chicago,  1897. 

Udden.  J.  A.,  A  new  well  at  Rock  Island.  Illinois:  Am.  Geologist,  vol.  21,  pp.  199-200, 
1898. 

Rolfe,  C.  W.,  The  geology  of  Illinois  as  related  to>  its  water  supply:  Univ.  of  Illinois, 
Chem.  Survey  of  the  Waters  of  Illinois,  Rept.  1S97-1902,  pp.  41-56,  1903. 

Udden,  J.  A.,  Geological  classification  of  the  waters  of  Illinois:  Illinois  State  Geol. 
Survey  Bull.  10,  pp.  8-21,  1909,  and  Illinois  State  Water  Survey  Bull.  4,  pp.  8-21,  1909. 

Anderson,  C.  B.,  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol. 
Survey  Bull.  34,  1919. 

McClenahan,  W.  T.,  Predicting  the  results  of  deep  well  borings:  Illinois  Soc.  Engrs., 
Proc.,  vol.  38,  pp.  37-47,  1923. 

Habermeyer,  G.  C.,  Public  ground-water  supplies  in  Illinois:  Illinois  State  Water 
Survey  Bull.  21,  1925. 

2Thwaites,  F.  T.,  The  Paleozoic  rocks  found  in  deep  wells  in  Wisconsin  and  north¬ 
ern  Illinois:  Jour.  Geology,  vol.  31,  pp.  529-555,  1923. 

(9) 


10 


STRATIGRAPHY  ANI)  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


of  those  who  have  not  followed  all  of  the  changes  in  usage  of  geologic 
names,  a  table  (Table  1)  has  been  prepared,  in  which  the  use  of  for¬ 
mation  names  in  different  reports  on  Illinois  and  adjoining  states  is 
compared.  The  description  of  formations  in  this  report  is  confined 
to  data  from  well  logs  and  does  not  include  a  discussion  of  their  paleon¬ 
tology  and  exact  correlation.  Each  formation  is  illustrated  by  typical 
well  records  from  the  region  here  discussed.  In  quoting  records  by 
others  some  of  the  wording  has  been  slightly  changed  to  correspond  with 
the  usage  in  the  data  collected  by  the  writer. 

Pennsylvanian  System 

MCLEANSBORO,  CARBONDALE,  AND  POTTSVILLE  FORMATIONS 

DESCRIPTION 

Rocks  of  the  Pennsylvanian  system  are  known  as  the  '‘Coal 
Measures”  or  the  Upper  Carboniferous.  Formations  of  this  age  under- 

Table  2. — Generalized  section  of  Pennsylvanian  rocks  of  La  Salle  Countya 


Description  of  strata  Thickness  Depth 

McLeansboro  formation  Feet  Feet 

Shale,  and  clay,  red,  yellow,  and  blue,  with  limestone 

nodules  .  24  24 

Coal  .  1  25 

Shale,  and  clay,  olive,  yellow,  and  black,  with  gray,  shaly 

limestone  .  19  44 

Coal  and  fire  clay .  1  45 

Shale,  blue  and  brown .  25  70 

Limestone,  gray  with  layers  of  blue  and  gray  shale .  29  99 

Limestone,  blue  .  5  104 

Shale,  hard,  black,  with  thin  coal  at  base .  7  111 

Shale,  blue,  with  layers  of  blue  limestone .  24  135 

Coal  and  fire  clay .  1  136 

Shale,  blue,  with  layers  of  gray  limestone .  69  205 

Shale,  brownish  red  to  brown,  with  thin  limestone  seams...  17  222 

Sandstone .  18  240 

Shale,  black,  slaty  and  in  part  sandy .  36  276 

Coal  and  fire  clay .  11  287 

Shale,  dark  brown .  16  303 

Sandstone .  34  337 

Carbondale  formation 

Shale,  black  .  10  347 

Coal  and  fire  clay .  10  357 

Shale,  sandy  .  30  387 

Sandstone,  varies  from  15  feet  to . •• .  35  422 

Shale,  brown,  olive,  blue,  gray,  and  black,  with  thin  layers 

of  shaly  limestone,  and  shaly,  calcareous  sandstone....  83  505 

Coal  and  fire  clay . 5  510 

Pottsville  formation 

Sandstone .  6  516 

Shale,  gray  and  dark  gray . 124  640 

Sandstone,  white  .  40  680 

Shale  light  gray .  36  716 

Sandstone,  fine  to  very  fine  grained,  gray .  20  736 

Shale,  blue  to  green,  sandy .  25  761 

Total  Pennsylvanian  761  feet 


^Adapted  from  Cady,  G.  H.,  Coal  resources  of  district  I  (Longwall) :  Illinois  Coal 
Mining  Investigations  Bull.  10,  pp.  124-126,  1015. 


System 

Northern  Illinois 

1927 

Noi 

Iowa,  1912e 
Minnesota,  1911/ 

Minnesota 

19000 

Devonian 

Sweetland  Creek 

Cedar  Valley 
Wapsipinicon 

Sweetland  Creek 

Cedar  Valley 
Wapsipinicon 

Hamilton 

Marcellus? 

Corniferous 

Silurian 

Niagaran 

Alexandrian 

Niag 

Alex, 

Niagara 

Ordovician 

Richmond  group 
Maquoketa 

Maqi 

Maquoketa 

Hudson  River 

Galena 

Decorah 

Platteville 

Galei 

Platt 

Galena 

Decorah 

Platteville 

Galena 

Trenton 

St.  Peter 

St.  E 

St.  Peter 

St.  Peter 

Prairie  du  Chien  group 
Shakopee 
“New  Richmond” 
Oneota 

Praii 

Sh 

Ne 

Or 

Shakopee 

New  Richmond 

Oneota 

Shakopee 

New  Richmond 

Lower  Magnesian 

Cambrian 

Jordan/ 

Jordan 

Jordan 

Trempealeau* 

St.  Lawrence 

St.  Lawrence 

Mazomanie 

Franconia 

Dresbach 

Jord 

Dresbach  and 
undifferentiated 
Cambrian 

Dresbach 

Eau  Claire 

St. 

Mt.  Simon 

Dre 

Hinckley 

B.,  The  artesian  waters  of  northefr  resources  of  Iowa:  U. 

29-1186,  1912. 


aAnderson,  C. 

II,  1919. 

ftDoes  not  show  new  geologic  systems  proposed  by 
Ulrich,  E.  O.,  Notes  on  new  names  in  table  ( 


Paleozoic  systems  in  Wisconsin:  Wisconsin  Acad.  Sc 


S.  Geol.  Survey  Water-Supply  Paper  293, 


ground  waters  of  southern  Minnesota:  U.  S.  Geol,  Survey  Water- 


— _  _  _  ~  vo*-  6’  ^aP  °*  s^e*  1901* 

Thwaites^F."  T\*,  ThePaTeozoic  rocks  found"  in  del  by  Ulrich;  it  is  the  opinion  of  the  writer  that  it  is  equivalent  to 

vol.  31,  pp.  529-555,  1923.  1  *  St.Lawrence.”  «  tt  a  n  t  cs 

cWeidman,  Samuel,  and  Schultz,  A.  It.,  The  undefoved  by  the  Board  of  Geologic  Names  of  the  U.  S.  Geol.  Survey. 

Geol.  and  Nat.  Hist.  Survey  Bull.  35,  PI.  II,  1915.  Part  of  Illinois. 
dChamberlin.  T.  C.,  Geology  of  Wisconsin,  vol. 


Table  1. — Correlation  table  of  geologic  names  used  in  Illinois  and  adjacent  states 


System 

Northern  Illinois 
1927 

Northeastern  Illinois 
1919a 

Wisconsin 

19 23  & 

Wisconsin 

1915c 

Wisconsin 
to  1915d 

Iowa,  1912® 
Minnesota,  1911/ 

Minnesota 

19000 

Devonian 

Sweetland  Creek 

Cedar  Valley 
Wapsipinicon 

Milwaukee 

Milwaukee  (Hamilton) 

Hamilton 

Sweetland  Creek 

Cedar  Valley 
Wapsipinicon 

Hamilton 

Marcellus? 

Corniferous 

Silurian 

Niagaran 

Alexandrian 

Niagaran 

Alexandrian 

Waubakee 

Niagaran  series — Guelph,  Ra¬ 
cine,  Waukesha,  Byron, 
Mayville 

Waubakee 

Niagaran  series 

Salina 

Niagara 

Niagara 

Ordovician 

Richmond  group 
Maquoketa 

Maquoketa 

Richmond  group 

Maquoketa 

Richmond  group 
Maquoketa 

Cincinnati 

Maquoketa 

Hudson  River 

Galena 

Decorah 

Platteville 

Galena 

Platteville 

Galena-Black  River  groups 
Galena 

Decorah 

Platteville,  Beloit 

Galena 

Decorah 

Platteville 

Galena 

Trenton 

Galena 

Decorah 

Platteville 

Galena 

Trenton 

St.  Peter 

St.  Peter 

St-  Peter 

St.  Peter 

St.  Peter 

St.  Peter 

St.  Peter 

Prairie  du  Chien  group 
Shakopee 
“New  Richmond” 
Oneota 

Prairie  du  Chien  group 
Shakopee 

New  Richmond 
Oneota 

Lower  Magnesian  group 
Shakopee 

Oneota 

Lower  Magnesian  group 
Shakopee 

Oneota 

Lower  Magnesian 

Shakopee 

New  Richmond 

Oneota 

Shakopee 

New  Richmond 

Lower  Magnesian 

Cambrian 

Jordan/ 

Madison 

Mendota,  Devils  Lake^ 

Jordan 

Madison  (Jordan) 

Madison 

Jordan 

Jordan 

Trempealeau* 

Mazomanie 

Franconia 

Trempealeau* 

Mendota  (St. Lawrence) 

Mendota 

St.  Lawrence 

St.  Lawrence 

Mazomanie 

Franconia 

Franconia 

Potsdam 

Dresbach 

Jordan/ 

Dresbach 

Dresbach 

Dresbach  and 
undifferentiated 
Cambrian 

Dresbach 

Eau  Claire 

St.  Lawrence 

Eau  Claire 

Eau  Claire 

Mt.  Simon 

Dresbach 

Mt.  Simon 

Mt.  Simon 

Hinckley 

oAnderson,  C.  B.,  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol.  Survey  Bull.  34,  Plate 
n,  i9i9. 

fcDoes  not  show  new  geologic  systems  proposed  by  Ulrich. 

Ulrich,  E.  O.,  Notes  on  new  names  in  table  of  formations  and  on  physical  evidence  of  breaks  between 
Paleozoic  systems  in  Wisconsin:  Wisconsin  Acad.  Sci.  Trans.,  vol.  21,  pp.  71-107,  1924. 

Thwaites,  F.  T.,  The  Paleozoic  rocks  found  in  deep  wells  in  Wisconsin  and  northern  Illinois:  Jour.  Geology, 
vol.  31,  pp.  529-555,  1923. 

cWeidman,  Samuel,  and  Schultz,  A.  R.,  The  underground  and  surface  water  supplies  of  Wisconsin:  Wisconsin 
Geol.  and  Nat.  Hist.  Survey  Bull.  35,  PI.  II,  1915. 

dChamberlin.  T.  C.,  Geology  of  Wisconsin,  vol.  1,  pp.  119-212,  1883. 


eNorton,  W.  H.,  et  al,  Underground  water  resources  of  Iowa:  U.  S.  Geol.  Survey  Water-Supply  Paper  293, 
PI.  II,  1912  ;  Iowa  Geol.  Survey,  vol.  21,  pp.  29-1186,  1912. 

/Hall,  C.  W.,  et  al,  Geology  and  underground  waters  of  southern  Minnesota:  U.  S.  Geol,  Survey  Water- 
Supply  Paper  256,  PI.  VI,  1911. 

^Winchell,  N.  H.,  Geology  of  Minnesota,  vol.  6,  Map  of  state,  1901. 

AThe  Mendota  is  assigned  to  this  position  by  Ulrich  ;  it  is  the  opinion  of  the  writer  that  it  is  equivalent  to 
the  lower  part  of  the  Trempealeau,  the  original  “St.  Lawrence.” 

iThe  name  Trempealeau  has  not  been  approved  by  the  Board  of  Geologic  Names  of  the  U.  S.  Geol.  Survey. 
/Formation  present  only  in  northwestern  part  of  Illinois. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


11 


lie  only  the  southern  part  of  the  area  here  described.  (See  fig.  1.)  They 
have  been  divided,  in  descending  order,  into  the  McLeansboro,  Carbon- 
dale,  and  Pottsville  formations  which  are  all  composed  of :  gray  to  black 
shale  which  is  in  part  calcareous,  and  much  of  which  is  very  pyritic ;  im¬ 
pure,  shaly,  brownish-gray,  pyritic,  calcareous  sandstone ;  gray,  calcitic 
limestones;  and  coal.  The  relative  proportions  of  these  rocks  vary  much 
within  short  distances.  The  thickness  reaches  a  known  maximum  of 
about  760  feet  in  this  region  but  is  much  less  in  most  of  the  area.  The 
generalized  section  in  Table  2  shows  the  character  of  the  Pennsylvanian 
formations. 

WATER  SUPPLIES 

The  greater  part  of  the  Pennsylvanian  rocks  are  impervious  or  yield 
little  water  the  quality  of  which  is  notoriously  poor.  In  all  but  a  few 
places  near  the  outcrop  of  a  water-bearing  layer,  salt  and  hydrogen  sul¬ 
phide  make  the  water  unfit  for  most  uses.  This  condition  is  apparently 
explained  by  (1)  the  discontinuity  of  the  porous  strata  which  has  pre¬ 
vented  thorough  flushing  of  the  soluble  minerals,  and  (2)  the  presence 
of  pyrite  and  carbon.  Inasmuch  as  the  Pennsylvanian  rocks  rest  upon 
several  of  the  underlying  formations,  the  water  in  the  latter  is  contam¬ 
inated  in  many  localities  which  are  adjacent  to  such  contacts.  Explora¬ 
tion  for  potable  water  in  the  Pennsylvanian  rocks  and  in  formations 
which  are  in  contact  with  water-bearing  layers  in  them  cannot  be  recom¬ 
mended  where  other  sources  are  possible. 

DRILLING  CONDITIONS 

Most  of  the  Pennsylvanian  rocks  offer  no  unusual  difficulty  to  well 
drilling  so  far  as  the  experience  of  the  writer  has  shown.  Some  of  the 
shales,  particularly  the  fire  clays,  swell  or  disintegrate  to  clay  when  wet 
but  most  of  the  rocks  do  not  cave  to  an  unusual  extent.  Locally  old 
caved  mine  workings  may  be  encountered.  On  account  of  the  character 
of  the  water  it  is  absolutely  necessary  to  case  off  all  of  the  Pennsyl¬ 
vanian  formations. 


Devonian  System 

SWEETLAND  CREEK  SHALE,  CEDAR  VALLEY  LIMESTONE,  AND  WAPSIPINICON 

LIMESTONE 

Devonian  rocks  outcrop  only  in  the  vicinity  of  Rock  Island.  They 
consist  of  brown  and  black  shale,  and  white,  gray,  and  blue,  more  or  less 
shaly  limestones  and  dolomites.  The  total  thickness  does  not  exceed 
300  feet.  These  rocks  contain  some  water  near  the  base  especially  in 
Mercer  County.  They  offer  no  unusual  drilling  difficulty.  The  log  in 
Table  3  may  include  some  of  the  underlying  Silurian. 


12 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


Table  3. — JV ell  log  illustrating  character  of  Devonian  rocks 


Partial  log  of  city  well  No.  2,  Aledo,  Mercer  County 


Thickness  Depth 
Feet  Feet 


135 

Shale,  brownish  gray,  fossiliferous .  130  265 

Dolomite,  light  gray,  dark  spots,  pyritic,  in  part  oolitic,  fos¬ 
siliferous  . 20  285 

Limestone,  light  gray  . 65  350 

Shale,  light  gray  .  5  355 

Limestone,  light  gray  .  10  365 

Dolomite,  light  gray  to  white .  63  428 

Shale,  gray,  dolomitic,  logged  as  “black  slate” .  2  430 


Total  Devonian  295  feet 


Silurian  System 

NIAGARAN  DOLOMITE,  KANKAKEE  LIMESTONE,  AND  EDGE  WOOD  FORMATION 

(NIAGARAN  AND  ALEXANDRIAN  SERIES ) 

DESCRIPTION 

The  rocks  of  the  Niagaran  and  Alexandrian  series  of  northern  Illi¬ 
nois  consist  mainly  of  light  gray,  more  or  less  cherty  dolomite.  Toward 
the  base,  in  the  Alexandrian  series,  there  are  interstratified  beds  of  green, 
pink,  red,  and  blue  dolomitic  shales.  These  lower  beds  have  been  divided 
by  Savage4  into  the  Kankakee  limestone  and  the  Edgewood  formation. 
From  the  standpoint  of  the  well  driller  it  is  hardly  worth  while  to  at¬ 
tempt  to  distinguish  these  thin  formations  but  the  base  of  the  Silurian 
may  be  fixed  at  the  bottom  of  the  light-colored  dolomites.  The  total 
thickness  of  the  Silurian  nowhere  exceeds  500  feet  and  in  the  vicinity  of 
Chicago  is  much  less  than  that.  The  well  logs  in  Table  4  indicate  the 
character  of  the  formations  in 'various  parts  of  the  district. 

Table  4. — IV ell  logs  illustrating  character  of  Silurian  rocks 


(a)  Partial  log  of  city  well  No.  2,  Aledo,  Mercer  County 


Thickness 

Depth 

Feet 

Feet 

430 

Dolomite,  light  gray . 

.  25 

455 

No  sample,  log  shows  same  as  above . 

.  10 

465 

Dolomite,  bluish-gray,  vesicular . 

.  10 

475 

Dolomite,  light  gray . 

.  85 

560 

Total  Niagaran  130  feet 


4Savage,  T.  E.,  Alexandrian  rocks  of  northeastern  Illinois  and  eastern  Wisconsin: 
Bull.  Geol.  Soc.  America,  vol.  27,  pp.  305-324,  1916. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


13 


(b)  Partial  log  of  well  No.  2,  Mineral  Point  Zinc  Company, 

Depue,  Bureau  County a 


Thickness  Depth 

Feet  Feet 

388 

Dolomite,  white  .  10  398 

Dolomite,  dense,  light  gray .  17  415 

Dolomite,  white,  pyritic  .  7  422 

Dolomite,  light  gray,  some  white  chert . ...........  13  435 

Dolomite,  white,  porous,  white  chert  and  quartz .  35  470 

Dolomite,  white,  soft,  fine-grained,  some  quartz  and  white  chert  50  520 

Dolomite,  gray  and  greenish  gray,  soft,  some  green  clay .  20  540 

Dolomite,  white,  soft,  fine-grained,  white  chert .  15  555 

Dolomite,  light  gray,  soft,  white  chert .  47  602 

Dolomite,  coarse-grained,  buff  .  6  608 

Dolomite,  coarse-grained,  buff,  some  dark  gray  and  pyritic....  7  615 

Dolomite,  dense,  light  yellow,  with  some  white  rock,  fossiliferous  17  632 

Dolomite,  light  gray,  porous,  coarse-grained . 18  650 

Dolomite,  fine-grained,  white  .  23  673 

Dolomite,  buff,  with  some  gray  staining .  27  700 

Dolomite,  dense,  white  .  20  720 

Dolomite,  buff,  coarse-grained,  porous .  17  737 

Dolomite,  gray,  with  some  green  and  gray  shale .  28  765 

Dolomite,  gray  to  white,  some  white  chert .  77  842 

Dolomite,  gray,  pyritic  .  8  850 

Total  Silurian  (possibly  including  some  Devonian)  479  feet 


aUdden,  J.  A.,  Some  deep  borings  in  Illinois:  Illinois  State  Geol.  Survey  Bull.  24.  p. 
49,  1914. 


(c)  Partial  log  of  well  of  Abbott  Laboratories,  North  Chicago,  Lake  County 


100 

Dolomite,  light  gray,  porous  .  10  110 

Dolomite,  white  .  80  190 

Dolomite,  gray,  some  dark  gray  clay .  20  210 

Shale,  gray,  very  dolomitic .  20  230 

Dolomite,  light  gray  .  25  255 

Dolomite,  pink  to  pinkish  gray .  25  280 

Dolomite,  light  gray  .  65  345 

Dolomite,  light  and  dark  gray .  5  350 

Total  Niagaran  250  feet 


(d)  Partial  log  of  A.  D.  Lasker  well,  Everett,  Lake  County 


154 

Dolomite,  white  to  gray  .  39  193 

Dolomite,  white  to  light  gray,  with  white  chert .  35  228 

Dolomite,  light  gray  . 20  248 

Dolomite,  light  gray,  with  white  chert .  5  253 

Dolomite,  light  gray  and  greenish  gray .  5  258 

Dolomite,  light  gray  with  brown  spots;  white  chert .  10  268 

Dolomite,  white  to  light  gray .  90  358 

Dolomite,  dark  gray  to  white .  5  363 

Dolomite,  light  gray,  pyritic .  15  378 

Shale,  green,  dolomitic;  dolomite,  light  gray .  5  383 

Dolomite,  light  gray  .  5  388 

Dolomite,  light  gray  and  light  greenish  gray .  10  398 

Total  Niagaran  and  Alexandrian  244  feet 


14 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN'  ILLINOIS 


WATER  SUPPLIES 

The  Silurian  dolomites  yield  water  mainly  from  cracks  and  to  some 
extent  from  openings  caused  by  solution.  Quantities  of  as  much  as  1,100 
gallons  per  minute  have  been  reported  in  some  localities  but  these  are 
exceptional.  The  amount  of  water  depends  upon  the  local  amount  of 
fracturing  of  the  formation.  Near  Chicago  the  water  of  many  wells 
contains  hydrogen  sulphide.5  In  some  localities  there  are  strong  show¬ 
ings  of  oil  whose  presence  renders  the  water  undrinkable.  Exploration 
for  oil  was  once  carried  on  in  and  near  Chicago  without  securing  com¬ 
mercial  production.6  In  later  years  a  little  oil  and  gas  were  found  near 
Lake  Forest.7.  In  view  of  the  lack  of  an  impervious  capping  over  the 
dolomite  and  the  universal  presence  of  fresh  water  which  implies  thor¬ 
ough  flushing  of  the  formation,  it  is  extremely  unlikely  that  any  large 
quantity  of  either  oil  or  gas  will  ever  be  discovered.  According  to  an 
average  of  31  analyses8  the  Xiagaran  waters  of  Cook  County  average 
less  than  0.7  pound  of  encrusting  solids  per  1000  gallons  and  are  there¬ 
fore  decidedly  softer  than  the  water  of  Lake  Michigan  which  carries 
slightly  more  than  one  pound  in  the  same  quantity.  Near  La  Salle, 
water  with  as  little  encrusting  solid  but  considerable  salt  is  ascribed  to 
the  same  formation9  but  such  soft  waters  are  not  typical.  Most  Xiagaran 
waters  contain  more  than  3  pounds  of  encrusting  solids  per  1000  gallons. 
Anderson10  mentions  several  wells  which  were  contaminated  by  the 
effluent  from  gas  works,  so  that  sewage  contamination  is  possible  in  all 
wells  where  the  glacial  drift  is  thin  or  pervious. 

DRILLING  CONDITIONS 

No  unusual  drilling  conditions  are  likely  to  exist  in  the  Silurian 
dolomites  except  incline  fissures  which  may  cause  a  crooked  hole. 
When  an  intercepting  tunnel  was  constructed  at  Argo  to  cut  a  number 
of  wells  at  a  depth  of  357  feet  the  holes  were  all  found  to  be  out  of 
vertical  by  amounts  ranging  from  6  inches  to  11  feet.11  It  is  recom¬ 
mended  that  all  wells  in  large  cities  where  the  drift  is  thin  be  cased 
through  the  Silurian  rocks  in  order  to  eliminate  the  danger  of  contam¬ 
ination  as  well  as  the  objectionable  hydrogen  sulphide. 

5  Wei  land,  H.  J..  and  Bartow.  Edward.  Hydrogen  sulphide  in  the  well  waters  of  Chi¬ 
cago  and  vicinity:  Illinois  State  Water  Survey  Bull.  13,  pp.  359-368.  1916. 

sShufeldt,  G.  A.,  On  an  oil-well  boring  at  Chicago:  Am.  Jour.  Sci.,  zd  ser.,  vol  40, 
pp.  388-389,  1865. 

Hunt,  T.  S.,  On  the  oil-bearing  limestone  of  Chicago:  Canadian  Naturalist,  vol.  6, 
pp.  54-59,  1871. 

Grant,  U  S.,  Possible  horizons  for  oil  and  gas  in  northeastern  Illinois:  Illinois  State 
Acad.  Sci.  Trans.,  vol.  15,  pp.  389-392,  1922. 

Alden,  W.  C.,  U.  S.  Geol.  Survey  Geol.  atlas,  Chicago  folio  (No.  81),  p.  13,  1902. 

7Anderson,  C.  B..  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol. 
Survey  Bull.  34,  pp.  185-186,  1919. 

sidem,  p.  96. 

9Cady,  G.  H.,  Geology  and  mineral  resources  of  the  Hennepin  and  Ea  Salle  quad¬ 
rangle:  Illinois  State  Geol.  Survey  Bull.  37,  p.  126,  1919. 

lOAnderson,  C.  B..  op.  cit.,  p.  103. 

nAnonymous,  Corn  products  water  supply  and  underground  pumps:  Engr.  News- 
Record,  vol.  93,  pp.  501-503.  1924. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


15 


Ordovician  System 

MAOUOKETA  SHALE  (RICHMOND  GROUP) 

DESCRIPTION 

The  Maquoketa  formation  consists  of  bluish  gray  to  greenish  gray, 
rarely  brown  dolomitic  shale  with  subordinate  amounts  of  white  to  dark 
gray  or  blue  dolomite,  some  of  which  is  very  shaly.  In  far  northwestern 
Illinois  there  are  some  layers  of  calcitic  limestone.  The  thickness  varies 
from  about  100  feet  to  nearly  200  feet.  No  attempt  has  yet  been  made 
to  subdivide  the  formation.  The  amount  of  water  is  negligible.  The  well 
logs  in  Table  5  indicate  the  character  of  the  Maquoketa. 


Table  5. — Well  logs  illustrating  character  of  the  Maquoketa  shale 


(a)  Partial  log  of  village  well,  Grays  Lake,  Lake  County 


Thickness  Depth 
Feet  Feet 


400 

Shale,  blue,  dolomitic  .  30  430 

Dolomite,  dark  gray,  and  shale,  blue,  dolomitic .  10  440 

Shale,  blue,  dolomitic  .  30  470 

Dolomite,  dark  gray  with  light  gray  spots .  20  490 

Shale,  blue,  dolomitic .  60  550 

Total  Maquoketa  150  feet 


(b)  Partial  log  of  A.  D.  Lasker  well,  Everett,  Lake  County 


398 

Shale,  blue,  dolomitic  .  25  423 

Dolomite,  gray  and  dark  blue,  pyritic .  20  443 

Shale,  dark  blue,  hard,  dolomitic;  dolomite,  gray .  5  448 

Shale,  blue,  dolomitic  .  80  528 

Total  Maquoketa  130  feet 


(c)  Partial  log  of  well  drilled  for  Chicago  Portland  Cement  Company 

Oglesby,  La  Salle  Countyrt 


Shale,  gray,  calcareous  . 

Limestone,  gray,  somewhat  shaly  . 

Limestone,  gray,  subcrystalline  . 

Limestone,  gray  to  bluish  gray . 

Shale,  gray,  rather  soft  . 

Dolomite,  gray,  subcrystalline,  some  shale 

Dolomite,  gray,  subcrystalline  . 

Limestone,  gray,  subcrystalline  . 

Shale,  gray,  slightly  calcareous  . 

Shale,  gray,  calcareous  . 

Total  Maquoketa  165  feet 


5 

985 

990 

10 

1000 

20 

1020 

20 

1040 

20 

1060 

25 

1085 

25 

1110 

15 

1125 

15 

1140 

10 

1150 

aCady,  G.  H.,  Coal  resources  of  district  I  (Long wall) :  Illinois  Coal  Mining-  Investiga¬ 
tions  Bull.  10,  p.  127,  1015.  This  log  is  based  upon  study  of  samples  by  T.  E.  Savage; 
another  log,  stated  slightly  differently,  is  given  in  a  later  publication,  Cady,  G.  H.,  Geol¬ 
ogy  and  mineral  resources  of  the  Hennepin  and  La  Salle  quadrangles:  Illinois  State  Geol. 
Survey  Bull.  37,  p.  30,  1919. 


16 


STRATIGRAPHY  ANI)  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


(d)  Partial  log  of  city  well  No.  2,  Aledo,  Mercer  County 


Thickness  Depth 
Feet  Feet 


560 

Shale,  blue,  dolomitic .  73  633 

Dolomite,  gray  and  blue,  pyritic .  15  648 

Shale,  blue,  dolomitic  .  50  698 

Shale,  light  brown,  dolomitic  .  35  733 

Shale,  brown,  very  dolomitic,  hard .  10  743 

Total  Maquoketa  183  feet 


DRILLING  CONDITIONS 

The  Maquoketa  shales  are  very  soft  and  drill  easily  but  at  times  it 
is  difficult  to  pick  up  the  mud  with  the  bailer.  Sand  or  gravel  poured 
into  the  hole  often  aids  drilling.  The  collection  of  accurate  samples  is 
difficult  because  some  of  the  cuttings  form  a  thin  mud  which  will  not 
settle.  Material  stuck  to  the  bit  is  not  reliable,  for  it  may  have  been 
scraped  from  the  side  of  the  hole  while  the  tools  were  coming  up. 
Masses  of  mud  often  stick  to  the  side  of  the  hole  and  later  fall  off. 
Washed  samples  are  misleading  since  the  dolomite  and  limestone  beds 
are  all  interbedded  with  more  or  less  shale.  The  entire  formation  should 
be  cased  off  and  it  is  best  to  place  the  casing  before  the  well  is  drilled 
any  deeper.  A  water-tight  joint  or  “shut-off”  must  be  made  at  the  bot¬ 
tom  of  this  string  of  pipe.  In  most  wells  this  may  be  accomplished  by 
the  use  of  a  shoe,  for  enough  mud  will  settle  around  the  pipe  to  seal  it. 
The  shut-off  may  be  tested  by  bailing  down  the  Avater  inside  the  pipe 
to  a  level  that  is  lower  than  it  was  before  casing  and  watching  the  level 
over  night  to  see  that  it  is  substantially  stationary.  Failures  to  effect  a 
shut-off  have  been  known  to  be  due  either  to  a  crooked  hole  or  to  the 
fractures  in  the  rock  on  which  the  bottom  of  the  casing  rested.  The 
difficulty  can  be  overcome  by  either  drilling  deeper  to  form  a  new  shoul¬ 
der  or  feeding  mud  or  cement  down  the  outside  of  the  pipe  while  the 
water  inside  is  bailed  down. 

GALENA  AND  PLATTEVILLE  FORMATIONS  (TRENTON  AND  BLACK  RIVER  GROUPS) 

DESCRIPTION 

The  Trenton  group  is  represented  in  northern  Illinois  by  the  Galena 
dolomite.  This  formation  consists  of  gray,  cherty,  coarse-grained  dolo¬ 
mite  which  weathers  at  the  surface  to  a  yellow  sand-like  consistency. 
Below  the  Galena  in  northwestern  Illinois  is  a  few  feet  of  shale  which  is 
equivalent  to  the  Decorah  shale  of  Minnesota  and  Wisconsin.  Beneath 
this  shale,  which  is  generally  bituminous,  is  the  Platteville  formation  of 
the  Black  River  group.  In  the  west  this  formation  is  calcitic  limestone; 
to  the  east  it  gives  way  to  dolomite  of  gray  and  blue  colors,  the  equiv¬ 
alent  of  the  Beloit  formation  of  Wisconsin.  In  the  northwestern  and 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


17 


central  parts  of  the  State,  the  base  of  the  Platteville  is  marked  by  a 
brown  and  green  shale  and  sandstone,  the  Glenwood  member;12 
farther  east  it  is  marked  by  coarse-  to  medium-grained,  dolomitic  sand¬ 
stone.  Locally  a  layer  of  very  dolomitic  sandstone  with  a  maximum 
thickness  of  40  feet  is  found  in  the  basal  Platteville.  This  “stray  sand” 
is  separated  from  the  St.  Peter  sandstone  by  10  feet  or  more  of  some 
what  sandy,  gray  dolomite.  The  basal  Platteville  is  very  pyritic.  The 
thickness  of  the  Galena  and  Platteville  formations  combined  varies  from 
a  little  less  than  300  feet  to  as  much  as  450  feet.  The  well  logs  in  Table 
6  show  the  character  of  these  formations  which  are  not  everywhere 
easily  separated. 


Table  6. — Well  logs  illustrating  character  of  Galena  and  Platteville  formations 


(a)  Partial  log  of  well  of  Clinton  Brewing  Company,  Clinton,  Iowa® 


Galena  formation 

Dolomite,  gray,  crystalline,  in  part  cherty . 

Dolomite,  gray,  cherty  . 

Dolomite,  gray  or  light  buff;  crystalline;  in  part  vesicular.. 
Dolomite  or  magnesian  limestone,  brown,  crystalline;  with 
fossiliferous  bituminous  shale . 

Decorah  (?) 

Shale,  brown,  highly  bituminous  and  fossiliferous . 

Platteville  formation 

Limestone,  magnesian,  brown  . 

Limestone,  magnesian,  dark  gray,  subcrystalline,  in  part 

cherty  . 

Limestone,  bluish  gray,  dense,  fossiliferous,  thin  bedded... 

Limestone,  light  yellowish  gray,  soft,  fossiliferous . 

Limestone,  light  bluish  gray,  fossiliferous . 

Shale,  brown,  bituminous;  and  limestone,  dense . 

Shale,  bluish  green,  pyritic,  flaky . 


Thickness 

Depth 

Feet 

Feet 

330 

170 

500 

10 

510 

55 

565 

5 

570 

5 

575 

12 

587 

33 

620 

25 

645 

5 

650 

5 

655 

10 

665 

5 

670 

Total  Galena-Platteville  340  feet 


aNorton,  W.  H.,  et  al,  Underground  water  resources  of  Iowa:  U.  S.  Geol.  Survey 
Water-Supply  Paper  293,  p.  391,  1912. 


(b)  Partial  log  of  city  well  No.  2,  Aledo,  Mercer  County 


Dolomite,  light  brown-  to  gray . 

Dolomite,  light  gray  . 

Dolomite,  light  gray  with  some  white  chert 

Dolomite,  white,  white  chert,  pyritic . 

Dolomite,  brown  and  gray,  pyritic . 

Shale,  greenish  gray,  dolomitic . 

Limestone,  brown,  blue,  and  white . 

Dolomite,  gray,  blue  spots . 

Total  Galena-Platteville  322  feet 


743 

20 

763 

102 

865 

85 

950 

15 

965 

30 

995 

5 

1000 

10 

1010 

55 

1065 

i2Bevan,  Arthur,  The  Glenwood  as  a  horizon  marker  at  the  base  of  the  Platteville 
limestone:  Illinois  State  Geol.  Survey  Rept.  of  Investigations  No.  9,  p.  6,  1926. 


18 


STRATIGRAPHY  AM)  GEOLOGIC  STRUCTURE  OF  NORTHERN'  ILLINOIS 


(c)  Partial  log  of  well  drilled  for  Chicago  Portland  Cement  Company, 

Oglesby,  La  Salle  County^ 


1150 

Dolomite,  gray,  fine  grained .  35  1185 

Limestone,  magnesian,  gray  .  40  1225 

Limestone,  gray,  fine  grained,  some  magnesium .  85  1310 

Limestone,  gray,  fine  grained  .  55  1365 

Limestone,  gray,  very  fine  grained .  120  1485 

Limestone,  dark  gray  to  light  gray,  very  fine  grained .  10  1495 

Limestone,  gray,  fine  grained  .  25  1520 

Total  Galena-Platteville  370  feet 


ibCady,  G.  H.,  Coal  resources  of  district  I  (Longwall):  Illinois  Coal  Mining  Investi¬ 
gations  Bull.  10,  pp.  127-128,  1915.  Log  based  on  examination  of  samples  by  T.  E.  Savage; 
a  different  log  was  published  by  Cady  at  a  later  date. 


(d)  Partial  log  of  village  well,  Grays  Lake,  Lake  County 


Thickness  Depth 
Feet  Feet 


550 

Dolomite,  gray  .  100  650 

Dolomite,  gray,  with  a  few  blue  spots .  40  690 

Dolomite,  gray  and  buff,  some  blue  spots;  white  chert .  10  700 

Dolomite,  gray,  with  blue  spots;  white  chert .  40  740 

Dolomite,  gray,  with  some  blue  layers .  10  750 

Dolomite,  dark  gray,  with  blue  spots .  50  800 

Dolomite,  light  gray,  dark  gray,  blue  and  buff .  30  830 

Dolomite,  dark  gray,  with  blue  spots .  10  840 

Sandstone,  medium  grained,  white,  calcareous .  10  850 

Sandstone,  fine  grained,  white,  calcareous;  thin  layers  of  gray, 

calcareous  shale  .  30  880 

Dolomite,  light  bluish,  gray,  very  pyritic .  10  890 

Sandstone,  very  coarse,  white;  dolomite  layers  like  above .  10  900 

Total  Galena-Platteville  350  feet 


WATER  SUPPLIES 

Except  on  the  outcrop,  and  along  the  La  Salle  anticline  where  there 
has  been  much  Assuring,  the  Galena  and  Platteville  formations  yield 
little  water.  On  account  of  the  presence  of  pyrite,  the  Avater  contains 
considerable  amounts  of  sulphates  ;  this  fact  explains  the  very  hard  scale 
formed  when  waters  from  these  formations  are  used  in  boilers.  Because 
of  the  comparative  thinness  of  the  formations,  it  is  rarely  advisable  to 
stop  drilling  before  the  underlying  St.  Peter  sandstone  is  reached.  Shows 
of  oil  are  not  at  all  uncommon ;  a  notable  instance  was  reported  at  the 
Crotian  Orphanage  east  of  Des  Plaines.  There  is  a  remote  possibility  of 
commercial  production  of  oil  should  domes  be  discovered  on  the  crest 
of  the  anticline  north  and  northwest  of  Des  Plaines,  but  it  is  probable 
that  almost  all  of  the  oil  that  was  once  present  has  been  washed  out  by 
fresh  water. 


DRILLING  CONDITIONS 

Unless  it  is  desired  to  shut  off  some  of  the  lower  sandstones,  the 
hole  through  the  Galena  and  Platteville  formations  may  be  left  uncased. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


19 


Presence  of  sand  in  the  cuttings  gives  warning  of  the  near  approach  to 
the  St.  Peter  sandstone.  The  “stray  sand"  should  not  be  mistaken  for 
the  St.  Peter.  It  is  coarser  grained  and  more  dolomitic  than  the  St. 
Peter,  breaks  in  chips,  and  contains  no  chert  or  red  non-dolomitic  shale. 
In  disturbed  zones,  as  near  Des  Plaines  and  La  Salle,  caving  rock  may 
be  found  in  these  formations. 

ST.  PETER  SANDSTONE 
DESCRIPTION 

As  found  in  wells,  St.  Peter  is  a  light  gray,  less  commonly  pink 
or  yellow,  fine-  to  medium-grained,  more  or  less  dolomitic  sandstone. 
A  layer  a  few  inches  thick  which  is  cemented  by  marcasite,  a  variety 
of  iron  sulphide,  is  found  at  the  top  in  many  places.  Beneath  the  sand¬ 
stone,  which  was  originally  defined  as  the  St.  Peter  formation,  is  a 
variable  thickness  of  red  and  green  shale  with  pebbles  of  white  and  yel¬ 
low  chert,  sandstone  with  chert  pebbles,  and  some  pink  and  gray  dolo¬ 
mite.  In  some  places  only  the  chert-sandstone  conglomerate  is  found. 
These  basal  beds  were  formerly  referred  to  the  Prairie  du  Chien  forma¬ 
tion  but  as  they  are  material  formed  by  its  weathering  and  then  re¬ 
worked  by  water  it  seems  preferable  to  assign  them  to  the  younger 
formation.  Including  these  beds,  the  thickness  of  the  enlarged  St.  Peter 
varies  from  50  to  nearly  500  feet.13  In  Wisconsin  the  absence  of  the 
St.  Peter  at  many  places  is  determined  from  rock  outcrops  and  well 
records  based  on  the  study  of  samples.  It  is  possible  that  it  is  absent  in 
parts  of  Illinois  since  it  is  very  thin  in  the  Sears  Roebuck  well  at  Chicago. 
Table  7  illustrates  the  character  of  the  St.  Peter. 

Table  7. —  Well  logs  illustrating  character  of  the  St.  Peter  sandstone 
(a)  Partial  log  of  city  well,  Galena,  Jo  Daviess  County 


Thickness  Depth 
Feet  Feet 


155 

Sandstone,  medium  grained,  very  light  gray,  pyritic .  50  205 

Sandstone,  medium  grained,  -light  gray  and  pink .  15  220 

Sandstone,  fine  grained,  light  yellow . 15  235 

Sandstone,  medium  grained,  pink,  yellow,  and  white,  no  sample 

265-275  . 50  285 

Sandstone,  pink;  with  red  shale .  30  315 

Sandstone,  brownish  red;  shale,  green  and  purple;  chert  and 

some  dolomite  .  20  335 

Shale,  purple  and  green  layers;  micaceous,  hard;  some  sand....  10  345 

Total  St.  Peter  190  feet. 


i3lf  the  record  of  an  old  well  at  Dixon  given  by  Tiffany  is  correct  this  figure  may 
reach  715  feet.  Tiffany,  A.  S.,  Record  of  deep  well  at  Dixon,  Illinois:  Am.  Geologist,  vol.  5» 
p.  124.  1890. 


20 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


(b)  Partial  log  of  Chicago  and  North  Western  Railway  well, 

Malta,  De  Kalb  County 


Sandstone,  medium  to  fine  grained,  gray,  dolomitic;  some  green 

shale  . 

Sandstone,  medium  to  fine  grained,  gray  to  white . 

Sandstone,  medium  to  fine  grained,  yellow  to  gray . 

Shale,  red;  pebbles  of  white  chert . 

Sandstone,  medium  to  coarse  grained,  pink;  pebbles  of  white 

chert  . 

Sandstone,  fine  to  medium  grained,  light  gray;  some  light  yel¬ 
low  quartzitic  layers  and  pebbles  of  white  chert . .  . 

Shale,  pink,  very  sandy;  many  pebbles  of  white  chert . 

Sandstone,  fine  grained  to  medium  grained,  gray  -  - . 

Conglomerate;  coarse  to  fine-grained  sandstone  with  pebbles  of 

white  chert  . 

Sandstone,  coarse  to  medium  grained,  pink,  shaly . 

Conglomerate,  coarse  to  medium  grained;  white  and  pink  sand¬ 
stone  with  pebbles  of  white  chert . 

Total  St.  Peter  460  feet. 


490 

• 

55 

545 

55 

600 

260 

860 

5 

865 

10 

875 

25 

900 

10 

910 

5 

915 

5 

920 

25 

945 

5 

950 

(c)  Partial  log  of  well  of  North  Shore  Country  Club,  Glenview,  Cook  County 


Thickness  Depth 
Feet  Feet 


840 

Sandstone,  fine  grained,  gray,  dolomitic  .  20  860 

Sandstone,  fine  grained,  gray  .  100  960 

Conglomerate,  pebbles  of  white  chert  in  coarse  to  fine  grained, 

gray  sandstone;  some  gray,  dolomitic  shale .  20  980 

Conglomerate  like  above  mixed  with  gray  dolomite  and  shale...  10  990 

Total  St.  Peter  150  feet. 


WATER  SUPPLIES 

The  St.  Peter  sandstone  is  an  important  water-bearing  formation 
near  its  outcrop  in  the  north-central  portion  of  the  State  but  no  longer 
yields  large  quantities  of  water  in  the  Chicago  district  because  of  (a)  its 
irregular  thickness  and  (b)  overdraft  by  the  numerous  wells  in  Chicago. 
As  a  result  of  oxidation  of  the  pyrite  and  marcasite  at  the  top  of  the 
formation  and  in  the  adjacent  dolomites,  the  water  contains  considerable 
sulphate  and  rarely  are  less  than  3  pounds  of  encrusting  solids  found 
in  1000  gallons.  Where  adjacent  to  water-bearing  layers  in  the  Penn¬ 
sylvanian,  as  east  of  La  Salle,  the  water  carries  some  hydrogen  sulphide. 
In  localities  where  the  St.  Peter  is  thick  and  wells  are  widely  separated, 
yields  of  200  gallons  per  minute  or  more  may  be  obtained. 

DRILLING  CONDITIONS 

The  top  and  bottom  of  the  St.  Peter  are  levels  at  which  an  unusual 
amount  of  trouble  may  be  encountered  in  drilling.  Many  strings  of  tools 
have  been  lost  soon  after  the  St.  Peter  has  been  entered.  Drilling  pro¬ 
ceeds  without  apparent  trouble  until  the  attempt  is  made  to  withdraw 
the  tools  which  are  then  found  to  be  stuck.  Drillers  ascribe  this  diffi¬ 
culty  to  the  fact  that  the  water  level  is  in  many  places  lower  in  the  St. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


21 


Peter  than  in  higher  formations  and  the  water  runs  down  the  hole  carry¬ 
ing  fine  cuttings  which  settle  around  the  tools  or  mud  up  the  walls  of 
the  hole.  Insertion  of  casing  from  the  surface  to  the  bottom  of  the 
Maquoketa  shale  with  care  to  secure  a  good  shut-off  is  said  to  remedy 
this  difficulty.  It  is  also  advisable  to  make  short  runs,  clean  the  hole 
thoroughly,  and  not  drill  continuously  when  the  St.  Peter  is  reached. 
Should  the  tools  be  lost,  it  is  almost  hopeless  to  attempt  to  withdraw 
them  without  clearing  away  as  much  of  the  debris  as  possible  by  drilling 
past  the  tools ;  this  cannot  be  accomplished  in  holes  much  smaller  than 
8  inches  in  diameter  since  there  is  not  room  enough  to  permit  the  tools 
to  swing  sideways.  An  objection  to  holes  less  than  6  inches  in  diameter 
is  that  efficient  fishing  tools  are  not  made  for  smaller  sizes.  The  only 
way  to  fish  a  five-inch  cable  drill  is  to  use  a  friction  socket  which  does 
not  take  a  firm  hold.  These  difficulties  do  not  apply  to  flowing  wells 
where  the  water  carries  away  the  cuttings.  The  reason  many  old  wells 
are  of  very  small  diameter  is  that  pole  tools  were  used  and  fishing  was 
easier  than  with  cable  tools.  Pole  tools  have,  however,  been  abandoned 
on  account  of  their  many  disadvantages. 

Another  danger  zone  is  the  shales  and  conglomerates  at  the  base  of 
the  St.  Peter.  These  can  generally  be  drilled  through  without  much 
caving,  but  unless  the  hole  is  cased  at  once  either  large  chunks  fall  in  or 
swelling  reduces  the  size  of  the  hole  enough  to  cause  trouble.  This 
horizon  is  known  to  well  drillers  as  “The  Cave”.  Examination  of  rocks 
that  have  fallen  into  wells  shows  that  the  formations  are  filled  with 
cracks  and  small  faults. 

It  is  difficult  to  determine  in  some  places  the  point  at  which  all  of 
this  kind  of  material  has  been  passed  through,  since  shale  beds  may 
be  found  in  the  underlying  dolomites.  In  some  wells  casing  has  ap¬ 
parently  not  been  inserted  at  once,  for  samples  from  underlying  forma¬ 
tions  are  contaminated  with  caved  shale  and  chert.  Most,  if  not  all,  of 
the  chert  ascribed  to  the  Cambrian  formations  by  some  students  of  well 
records  is  unquestionably  of  such  an  origin.  It  is  best  to  insert  casing 
which  rests  on  a  shoulder  as  soon  as  it  is  apparent  that  the  caving  zone 
is  safely  passed.  The  work  must  be  planned  to  allow  for  a  reduction  in 
the  size  of  the  hole  and  foresee  the  contingency  that  one  reduction  may 
not  be  enough.  Underreaming  in  these  formations  is  by  all  means  to  be 
avoided  as  it  is  very  slow  and  troublesome. 

SHAKOPEE,  “NEW  RICHMOND,”  AND  ONEOTA  FORMATIONS 

(PRAIRIE  DU  CHIEN  GROUP) 

DESCRIPTION 

The  Prairie  du  Chien  or  Lower  Magnesian  group  is  divided  in  de¬ 
scending  order  into  the  Shakopee  dolomite,  the  “New  Richmond”  sand- 


22 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


stone,  and  the  Oneota  dolomite.  These  subdivisions  cannot  as  yet  be 
made  in  all  parts  of  the  State  since  the  sandstone  which  separates  the 
dolomites  is  not  found  at  all  points.  In  part  the  irregularity  in  the  pres¬ 
ence  of  the  formations  is  accounted  for  by  pre-St.  Peter14  erosion  which 
locally  removed  the  entire  group  and  appears  to  have  destroyed  the 
Shakopee  formation  over  nearly  all  of  the  eastern  part  of  northern 
Illinois. 

The  dolomites  are  mainly  light  gray  in  color  but  red,  pink,  or  buff 
dolomite  is  found  in  some  localities.  White,  yellow,  and  pink  chert, 
both  oolitic  and  dense,  is  common  near  the  outcrop  but  is  much  less 
abundant  at  depth.  Thin  layers  and  specks  of  green  shale  are  wide¬ 
spread  and  locally  some  red  shale  is  found.  Some  layers  are  sandy  and 
quartz-lined  cavities  are  common.  Some  of  the  dolomite  breaks  under 
the  drill  into  small  regular  chips  which  have  been  mistaken  for  sand¬ 
stone  by  inexperienced  drillers.  It  is  an  open  question  whether  the 
medium-grained  dolomitic  sandstone  near  the  middle  of  the  group  in 
the  western  part  of  the  State  is  really  the  same  as  the  original  New 
Richmond  sandstone  of  Minnesota.  Near  Dixon  this  sandstone  con¬ 
tains  red  and  green  shale  together  with  chert.  It  is  difficult  to  fix  the 
base  of  the  group.  At  Glenview  there  is  a  sandstone  which  may  be  the 
Madison  formation  of  Wisconsin.  Some  of  the  purple-spotted  non- 
chertv  dolomite  of  the  basal  Prairie  du  Chien  of  northeastern  Illinois 
may  be  equivalent  to  the  Mendota  dolomite  of  Wisconsin  but  there  ap¬ 
pears  to  be  no  way  to  confirm  the  correlation.  If  it  is  correct,  the  Madi¬ 
son  sandstone  is  absent  in  most  of  Illinois.  In  this  report  no  attempt 
has  been  made  to  separate  these  beds  of  questionable  age  from  the  main 
body  of  the  Prairie  du  Chien.  In  former  reports  (Table  1)  this  group 
was  extended  downward  to  include  the  sandy  glauconitic  strata  here 
placed  in  the  Mazomanie  and  Franconia  formations.  The  strata  of  the 
Shakopee  are  in  many  places  irregularly  inclined,  closely  folded,  and 
complexly  faulted.  The  disturbances  which  caused  the  present  attitude 
of  the  beds  evidently  antedate  the  deposition  of  the  overlying  St.  Peter.15 
The  thickness  of  the  Prairie  du  Chien  group  as  defined  in  this  report 
reaches  a  maximum  of  about  400  feet.  In  certain  places,  as  at  Lom- 


i4According  to  Sardeson  (Sardeson.  F.  W.,  Shakopee  dolomite  and  its  cone  domes: 
Pan-Amer.  Geologist,  vol.  45,  pp.  29-48,  1926)  the  period  of  erosion  was  between  the 
deposition  of  the  Oneota  and  the  Shakopee  formations.  He  urges  that  the  Shakopee  con¬ 
sists  of  domes  of  dolomite  separated  by  sandstone  and  shale,  all  of  which  are  conform¬ 
ably  overlain  by  what  he  calls  the  “Peter”  sandstone.  It  is  a  fact  that  the  Shakopee 
strata  have  never  been  seen  to  be  truncated  by  the  St.  Peter  beds  but  instead  dip  parallel 
to  the  irregular  contact.  The  fact  is  indisputable  that  neither  Shakopee  nor  Oneota  dolo¬ 
mite  is  present  beneath  the  St.  Peter  in  many  localities  in  Wisconsin  and  that  the  basal 
St.  Peter  gives  indubitable  evidence  of  long  weathering  of  the  underlying  formations.  In 
Wisconsin  the  St.  Peter  is  known  to  rest  upon  all  formations  from  the  Shakopee  to  the 
Dresbach,  a  fact  supported  by  outcrops  and  by  well  logs.  Sardeson’s  claim  that  the  Prairie 
du  Chien  is  not  absent  at  Galena  because  he  has  collected  Shakopee  fossils  nearby  is  of 
no  weight  since  the  pinching  out  of  the  dolomites  takes  place  in  very  short  distances. 

loCady,  G.  H.,  The  structure  of  the  La  Salle  anticline:  Illinois  State  Geol.  Survey 
Bull.  36,  pp.  109-112,  1920. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


23 


bard,  Grays  Lake,  Rondout,  and  possibly  part  of  Dixon,  the  entire  group 
of  dolomites  is  absent  and  the  St.  Peter  rests  upon  the  Cambrian.  At 
Des  Plaines  no  “third”  dolomite  is  reported  in  the  city  well  but  its 
absence  may  be  the  result  of  faulting  since  the  rocks  are  very  much 
broken.  The  well  logs  in  Table  8  illustrate  the  character  of  this  group. 

Table  8. —  Well  logs  illustrating  character  of  the  Prairie  du  Chien  group 

(a)  Partial  log  of  well  of  Clinton  Brewing  Company,  Clinton,  Iowaa 


Thickness  Depth 
Feet  Feet 


730 

Shakopee  formation 

Dolomite,  gray,  sandy  .  23  753 

Dolomite,  gray;  with  layers  of  hard,  dark  gray  shale .  22  775 

Dolomite,  gray  to  bluish  gray,  pyritic .  18  793 

Sandstone,  medium-grained,  gray,  with  gray  dolomite .  7  800 

Dolomite,  light  gray,  dense,  cherty  and  shaly .  10  810 

Dolomite,  light  gray,  shaly,  sandy  .  15  825 

Dolomite,  light  to  dark  gray,  coarse  grained,  porous,  cherty  70  895 

New  Richmond  (?)  formation 

Dolomite,  light  gray,  sandy  .  16  911 

Sandstone,  light  gray,  dolomitic,  hard,  fine  grained .  9  920 

Oneota  formation 

Dolomite,  light  gray,  buff,  and  pink;  white  chert .  70  990 

Dolomite,  buff,  very  fine,  sandy .  10  1000 

Dolomite,  light  gray  to  bluish  gray;  cherty  and  sandy  in  . 

some  layers  .  75  1075 

Total  Prairie  du  Chien  345  feet. 


ctNorton,  W.  H.,  et  al,  Underground  water  resources  of  Iowa:  U.  S.  Geol.  Survey 
Water-Supply  Paper  293,  p.  391,  1912. 


(b)  Partial  log  of  well  No.  2,  Dixon  Epileptic  Colony,  near 

Dixon,  Lee  County 


Dolomite,  fine  grained,  red  and  gray;  top  part  caves . 

Dolomite,  fine  grained,  gray  . 

Dolomite,  fine  grained,  gray,  with  soft,  red,  caving  shale . 

Dolomite,  gray,  some  pink;  sandy  gray  pink,  and  yellow  chert 

in  part  oolitic  . 

Dolomite,  reddish  purple  and  brownish  gray;  some  white  chert.  . 
Sandstone,  medium  grained,  white;  shale,  green  and  dark  red, 

caving;  chert,  oolitic,  white  and  light  brown . 

Dolomite,  gray  to  light  brown  and  pink,  sandy;  some  red  and 
green  shale;  chert,  white  and  pink  with  quartz . 


Thickness 

Depth 

Feet 

Feet 

182 

8 

190 

61 

251 

11 

262 

143 

405 

37 

442 

18 

460 

140 

600 

Total  Prairie  du  Chien  418  feet 


(c)  Partial  log  of  well  of  North  Shore  Country  Club, 
Glenview,  Cook  County 


990 

Dolomite,  gray  .  80  1070 

Sandstone,  fine  grained,  gray,  very  dolomitic .  20  1090 

Dolomite,  gray,  sandy  . .  80  1170 

Total  Prairie  du  Chien  180  feet 


24 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


(d)  Partial  log  of  Mt.  Carmel  Cemetery  well,  Hillside,  Cook  County 


880 

Dolomite,  light  gray,  with  green  shale . . .  10  890 

Dolomite,  light  gray,  with  white  chert  and  green  shale .  10  900 

Dolomite,  light  gray,  with  some  green  shale .  20  920 

Dolomite,  light  gray,  with  white  chert .  10  930 

Dolomite,  light  gray  and  pink .  20  950 

Dolomite,  light  gray,  with  green  shale .  30  980 

Dolomite,  very  light  gray;  with  white  chert,  oolitic  and  dense.  .  .  20  1000 

Dolomite,  gray  and  pink,  sandy,  green  shade;  oolitic  white  chert  30  1030 

Dolomite,  gray,  sandy,  pyritic .  20  1050 

Dolomite,  light  gray,  with  green  shale .  60  1110 

Dolomite,  gray,  sandy  .  10  1120 

Dolomite,  light  gray  .  50  1170 

Dolomite,  light  gray,  pyritic  .  10  1180 

Dolomite,  gray,  some  glauconite .  10  1190 


Total  Prairie  du  Chien  310  feet,  beds  from  1110  to  1190 

possibly  Mendota 


WATER  SUPPLIES 

Where  deeply  buried  the  Prairie  du  Chien  dolomites  carry  little 
water.  Wells  formerly  in  use  to  supply  the  village  of  Utica  are  sup¬ 
posed  to  depend  for  their  supply  mainly  on  water  from  the  “New  Rich¬ 
mond”  sandstone  and  furnish  water  with  about  2.7  pounds  of  encrusting 
solids  per  1000  gallons.10  Other  wells  may  draw  a  portion  of  their  sup¬ 
ply  from  this  formation. 


DRILLING  CONDITIONS 

The  irregular  and  inclined  layers  near  the  top  of  the  Prairie  du  Chien 
group  where  the  Shakopee  dolomite  is  present  may  cause  much  trouble 
by  deflecting  the  hole.  In  some  places,  as  near  Dixon,  caving  layers  of 
shale  and  broken  dolomite  have  been  found  but  rarely  does  a  “cave" 
occur  which  is  sufficiently  bad  to  require  immediate  casing  with  reduc¬ 
tion  of  the  size  of  the  hole. 


Cambrian  System 

JORDAN  AND  TREMPEALEAU  FORMATIONS 

DESCRIPTION 

The  Jordan  and  Trempealeau  formations  are  so  closely  related  that 
they  can  be  discussed  together.  Formerly  the  Jordan  was  defined  as 
sandstone  and  the  Trempealeau  as  sandy  to  pure  dolomite  but  recently 
Ulrich17  has  endeavored  to  confine  the  name  Jordan  to  the  coarser 
grained  sandstone  just  beneath  the  Prairie  du  Chien  dolomite  excluding 
the  fine-grained  sandstone  below.  This  has  been  objected  to  by 

leCady,  G.  H.,  Geology  and  mineral  resources  of  the  Hennepin  and  La  Salle  quad¬ 
rangles:  Illinois  State  Geol.  Survey  Pull.  37,  pp.  124,  126,  1919. 

i7Ulrich,  E.  O.,  Notes  on  new  names  in  table  formations  and  on  physical  evidence  of 
breaks  between  Paleozoic  systems  in  Wisconsin:  Wisconsin  Acad.  Sci.  Trans.,  vol.  21,  pp. 
72-90.  1924. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


25 


Stauffer18  on  the  ground  that  it  conflicts  with  the  original  definition  of 
the  Jordan.  Irrespective  of  the  merits  of  the  controversy  the  older 
classification  is  preferable  from  the  standpoint  of  the  well  driller.  The 
Jordan  sandstone  thus  defined  is  medium-  to  fine-grained  and  is  wholly 
white  or  light  gray  in  color;  more  or  less  dolomite  is  present  and  to  both 
the  south  and  east  of  its  outcrop  in  western  Wisconsin,  northeastern 
Iowa,  and  southeastern  Minnesota  the  formation  grades  laterally  into 
sandy  dolomite.  The  maximum  thickness  of  the  Jordan  is  about  60  feet 
in  the  western  part  of  Illinois;  no  Jordan  can  be  distinguished  east  of 
Dixon.  The  Trempealeau  formation  consists  of  nearly  200  feet  of  more 
or  less  sandy  dolomite  of  gray,  pink,  and  brown  colors,  and  of  red  and 
gray  dolomitic  shale.  Some  glauconite  is  present.  The  thickness 
diminishes  to  the  east  and  no  Trempealeau  has  been  distinguished  east 
of  Dixon.  The  well  logs  in  Table  9  illustrate  the  character  of  the  Jordan 
and  Trempealeau  formations. 

WATER  SUPPLIES 

Although  the  Jordan  sandstone  is  very  important  as  a  source  of 
water  in  Iowa,  the  writer  does  not  know  of  any  large  wells  in  Illinois 
that  derive  a  significant  part  of  their  production  from  that  formation. 
The  nature  of  the  Trempealeau  formation  indicates  that  it  probably 
furnishes  little  water. 

MAZOMANIE  AND  FRANCONIA  FORMATIONS 

DESCRIPTION 

The  Mazomanie  and  Franconia  formations  consist  of  fine-  to 
medium-grained  sandstone  which  is  for  the  most  part  dolomitic  and 
glauconitic.  The  colors  are  gray,  green,  pink,  and  red.  In  the  far  west¬ 
ern  part  of  the  State  there  is  some  shale  and  sandy  dolomite.  In  the 

Table  9 — IV ell  logs  illustrating  character  of  the  Jordan  and  Trempealeau  formations 


(a)  Partial  log  of  well  of  Clinton  Brewing  Company,  Clinton,  Iowa® 


Thickness  Depth 
Feet  Feet 

1075 

Jordan  formation 

Sandstone,  fine  grained,  light  gray,  dolomitic,  glauconitic, 


with  layers  of  gray  dolomite . •  . .  15  1090 

Trempealeau  formation 

Dolomite,  light  gray,  fine  grained,  rounded  sand .  30  1120 

Sandstone,  light  gray,  very  fine  grained,  dolomitic .  20  1140 

Dolomite,  buff;  no  cuttings. recovered .  70  1210 

Dolomite,  light  brown,  hard,  medium  grained .  10  1220 

Dolomite,  some  sand  and  glauconite,  gray .  10  1230 

Dolomite,  sandy,  glauconitic,  pink .  10  1240 

Dolomite,  sandy,  gray  .  30  1270 

Dolomite,  light  pink,  sandy,  glauconitic  . .  • . .  10  1280 

Total  Jordan  and  Trempealeau  205  feet. 


aNorton,  W.  H.,  et  al,  Underground  water  resources  of  Iowa:  U.  S.  Geol.  Survey 
Water-Supply  Paper  293,  pp.  391-392,  1912. 

isstauffer,  C.  R.,  The  Jordan  sandstone:  Jour.  Geology,  vol.  33,  pp.  699-713,  1925. 


26 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


(b)  Partial  log  of  city  well,  Galena,  Jo  Daviess  County 


Jordan  formation 

Sandstone,  medium  grained,  white  to  gray,  pink  at  base-... 
Trempealeau  formation 

Dolomite,  fine  grained,  sandy,  brownish  gray  to  light  gray 
and  pink  . . . . . . 


435 

55  490 

120  610 


Total  Jordan  and  Trempealeau  175  feet 


Chicago  district  much  of  the  Mazomanie  has  been  logged  by  drillers  as 
either  “lime”  or  “sandy  lime”  but  examination  of  cuttings  leaves  no 
doubt  that  the  rock  is  sandstone  so  well  cemented  by  dolomite  that  it 
breaks  into  chips  under  the  drill.  Separation  of  the  Mazomanie  and  the 
underlying  Franconia  is  apparently  not  practicable  in  well  records;  the 
Mazomanie  contains  more  sand  and  dolomite  than  the  Franconia  which 
is  more  shaly.  There  is  probably  no  Franconia  in  the  eastern  half  of 
Illinois.  The  combined  formations  vary  in  thickness  from  about  80  to 
nearly  150  feet.  The  logs  in  Table  10  illustrate  the  character  of  these 
rocks. 


Table  10. —  Well  logs  illustrating  character  of  the  Mazomanie  and  Franconia  formations 


(a)  Partial  log  of  city  well,  Galena,  Jo  Daviess  County 


Thickness  Depth 
Feet  Feet 
610 

Shale,  light  to  medium  green,  slightly  gritty,  some  mica  and 


pyrite  .  10  620 

Shale,  green,  calcareous,  sandy,  glauconitic .  30  650 

Sandstone,  medium  grained,  gray,  glauconitic,  pyritic .  10  660 

Shale,  light  green,  slightly  calcareous,  sandy,  pyritic .  20  680 

Dolomite,  fine  grained,  brownish  gray,  sandy  glauconitic,  pyritic  10  690 


Total  Mazomanie  and  Franconia  80  feet 


(b)  Partial  log  of  city  well,  Clinton,  Iowaa 


Thickness  Depth 
Feet  Feet 


1355 

Dolomite,  pink,  very  fine,  sandy,  shaly,  glauconitic . . 1  1356 

Sandstone,  exceedingly  fine  grained,  shaly,  dolomitic;  dolomite, 

gray,  glauconitic  .  14  1370 

Sandstone,  fine  grained,  glauconitic,  with  green  shale .  30  1400 

Shale,  greenish  gray,  very  sandy,  glauconitic  .  40  1440 

Sandstone,  fine  grained,  glauconitic,  dolomitic;  shale,  sandy,  red  5  1445 


Total  Mazomanie  and  Franconia  90  feet 


aNorton,  W.  H.,  et  al..  Underground  water  resources  of  Iowa:  U.  S.  Geol.  Survey 
Water-Supply  Paper  293,  p.  385,  1912. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


27 


(c)  Partial  log  of  Chicago  and  North  Western  Railway  well, 
West  Chicago,  Du  Page  County^ 


1150 

Sandstone,  fine  grained,  gray  to  pink,  dolomitic,  with  red  dolo- 


mitic  shale  .  25  1175 

Sandstone,  fine  grained,  light  gray,  with  green  dolomitic  shale.  50  1225 

Sandstone,  coarse  to  medium  grained,  gray  to  white,  dolomitic, 

glauconitic,  breaks  in  chips  .  60  1285 

Total  Mazomanie  135  feet. 


bSamples  examined  by  R.  C.  Lentz,  inspector. 


(d)  Partial  log  of  well  at  St.  Mary’s  Academy,  Des  Plaines,  Cook  County 


860 

Dolomite,  gray  and  light  pink,  sandy,  glauconitic,  pyritic .  10  870 

Sandstone,  fine  grained,  pink,  very  dolomitic,  glauconitic,  pyritic, 

with  pink,  red,  and  green  dolomitic  shale...... .  15  885 

Sandstone,  fine  grained,  gray  and  pink,  very  dolomitic,  glauconitic  25  910 

Sandstone,  fine  to  very  fine  grained,  very  dolomitic,  glauconitic.  35  945 

Sandstone,  very  coarse  to  fine  grained,  with  some  pink  dolomite 

and  glauconite  . 20  965 

Total  Mazomanie  105  feet 


CORRELATION 

The  Jordan  sandstone  has  been  correctly  recognized  in  northeastern 
Iowa  and  northwestern  Illinois  for  a  long  time.  The  underlying  forma¬ 
tion  now  called  Trempealeau  was  called  St.  Lawrence  by  the  Iowa 
geologists.  The  sandstones  beneath,  now  recognized  as  Mazomanie  and 
Franconia,  were  included  under  the  name  St.  Lawrence.  In  north¬ 
eastern  Illinois  the  very  dolomitic  sandstone  here  referred  to  the  Mazo¬ 
manie  with  confidence  was  formerly  referred  to  the  basal  portion  of 
the  Prairie  du  Chien  group  (fig.  2),  although  Anderson19  was  some¬ 
what  uncertain  about  this  and  thought  possibly  these  strata  might 
correspond  with  the  Madison  and  Mendota  formations  of  Wisconsin. 
The  formations  in  question  are  characteristically  glauconitic,  and 
in  fact  constitute  the  most  prominent  glauconitic  horizon  in  the  entire 
section,  whereas  the  Madison  and  Mendota  are  both  low  in  glauconite. 
The  Madison  and  Mendota  are  everywhere  underlain  by  glauconitic 
sandstone  instead  of  the  pure  white  sandstone  which  is  beneath  the 
glauconitic  beds  of  northern  Illinois.  It  was  suggested  that  this  white 
sandstone  is  the  Jordan  but  no  place  is  known  where  the  Jordan  sand¬ 
stone  underlies  the  Mendota  dolomite.  The  succession  of  a  glauconitic- 
dolomitic  sandstone  underlain  by  a  white  sandstone  is  strikingly  like 
the  proved  Mazomanie-Dresbach  section  of  central  and  northeastern 
Wisconsin;  the  only  difference  is  that  the  Madison  sandstone  pinches 
out  to  the  south  of  Wisconsin  and  the  Jordan  sandstone  to  the  east  of 

lOAnderson,  C.  B.,  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol. 
Survey  Bull.  34,  pp.  84,  107,  1919. 


28 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


Iowa.  This  fact  is  made  certain  by  comparative  sections  drawn  across 
northern  Illinois  and  from  the  outcrops  in  Wisconsin  south  into  Illi¬ 
nois.20  In  addition,  the  formations  beneath  the  white  sandstone  here 
correlated  as  Dresbach  are  entirely  unlike  those  below  the  proved  Jor¬ 
dan  sandstone. 


WATER  SUPPLIES 

The  Mazomanie  and  Franconia  formations  are  for  the  most  part  too 
dense,  fine  grained,  and  dolomitic  to  furnish  much  water  except  where 
there  are  crevices.  Anderson21  reports  that  such  are  present  in  the 
vicinity  of  Chicago.  There  is  no  available  information  on  the  quality 
of  the  water. 


DRILLING  CONDITIONS 

No  unusual  drilling  difficulties  in  the  Mazomanie  and  Franconia 
formations  have  come  to  the  attention  of  the  writer.  Problems  arise 
when  it  is  desired  to  set  casing  to  the  bottom  of  the  Mazomanie  sand¬ 
stone.  The  rock  at  this  level  is  in  many  places  too  soft  to  support  the 
weight  of  the  pipe.  In  order  not  to  drill  too  deep  to  allow  of  making 
a  shoulder  on  a  firm  layer,  it  is  well  to  define  the  top  of  the  formation 
and  compute  its  base  from  records  of  thicknesses  in  adjacent  wells. 
The  top  of  the  Mazomanie  may  be  distinguished  by  the  presence  of  glau¬ 
conite,  a  dark  green,  soft  mineral  in  small  grains,  and  clear  quartz  sand 
in  amounts  making  up  a  considerable  portion  of  the  rock.  These  sub¬ 
stances  may  best  be  found  by  dissolving  the  cuttings  in  hydrochloric 
(muriatic)  acid  which  is  slightly  heated  in  a  glass  or  china  dish;  this 
treatment  will  cause  the  dolomite  to  dissolve  with  effervescence  of 
carbon  dioxide  and  the  quartz  and  glauconite  will  be  left  plainly  visible. 
Approach  to  the  bottom  of  the  Mazomanie  may  be  distinguished  by  the 
presence  of  very  coarse  quartz  grains  and  by  reduction  in  the  amount  of 
dolomite  which  is  made  manifest  by  less  effervescence  with  acid.  It  is 
the  opinion  of  the  writer  that  a  shut-off  may  best  be  made  when  the  first 
coarse  sandstone  is  reached  rather  than  at  the  true  base  of  the  forma¬ 
tion.  It  would  seem  advisable  to  explore  ahead  with  a  hole  of  smaller 
diameter  and  then  to  ream  down  to  a  shoulder  on  a  suitable  hard  layer. 

DRESBACH  SANDSTONE 
DESCRIPTION 

The  Dresbach  consists  of  medium-grained,  pure  white  to  yellow, 
or  rarely  pink  sandstone.  In  few  places  is  there  any  quantity  of  dolomite 
cement;  a  pink  or  yellow  layer  near  the  middle  of  the  formation  is  not 

2oThwaites,  F.  T.,  The  Paleozoic  rocks  found  in  deep  wells  in  Wisconsin  and  northern 
Illinois:  Jour.  Geology,  vol.  31,  pp  529-555,  1923. 

2iAnderson,  C.  B.,  op.  cit.,  pp.  86,  89. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


29 


SILURIAN 


ORDOVICIAN 


CAMBRIAN 


Fig.  2. 
correlation 


1 


Anderson’s 

correlation 

1919 


NIAGARAN 


ALEXANDRIAN 


MAQUOKETA 


Galena 

Platteville 


25 

w 

>—* 

S3 

O 

D 

Q 

09 

— 

cd 

•— < 

< 

od 

o, 


St.  Peter 


Shakopee 


New  Richmond 


Oneota 


Jordan 


< 

5 

03 

S 

<  ■< 

u 

ci 
09 
a. 
a. 

P 


St.  Lawrence 


Dresbach 


1  HE 


■i  r 


^=3§E- 


i  .J- 


i  r 


O  I 


I  I 


■  fl~4l 


Thwaites’ 

correlation 

1927 

NIAGARAN 

ALEXANDRIAN 

RICHMOND 

GROUP 

MAQUOKETA 

Galena 

Decorah 

Platteville 


SILURIAN 


St.  Peter 


Shakopee 


“New  Richmond” 


Oneota 


25 

09 

S3 

u 

Q 

09 
>— * 

cd 

«— 

< 

fu 


ORDOVICIAN 


Mazomanie 


Dresbach 


Eau  Claire 


Mt.  Simon 


CAMBRIAN 


LIMESTONE  CHERT 


SHALE  SANDSTONE 


Diagrammatic  columnar  section  of  northeastern  Illinois  showing  revised 
of  strata. 


30 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


uncommon.  The  top  of  the  formation  is  easily  recognized  by  the 
change  in  the  color  as  well  as  by  the  softness  of  the  rock.  The  thick¬ 
ness  varies  from  30  feet  near  Waukegan  to  nearly  200  feet  to  the  south 
and  west  of  that  point.  The  logs  in  Table  11  illustrate  the  character 
of  the  Dresbach. 


I  able  11. — Well  logs  illustrating  character  of  the  Dresbach  sandstone 


(a)  Partial  log  of  city  well,  Galena,  Jo  Daviess  County 


Thickness  Depth 
Feet  Feet 


700 

Sandstone,  medium  grained,  white .  40  740 

Sandstone,  rather  fine  grained,  light  gray .  100  840 

Total  Dresbach  140  feet 


(b)  Partial  log  of  city  well,  Clinton,  IowTaa 


1445 

Sandstone,  coarse  grained,  white .  5  1450 

Sandstone,  fine  grained,  white .  5  1455 

Sandstone,  coarse,  pinkish  gray  . .  20  1475 

Sandstone,  fine  grained,  white .  35  1510 

Total  Dresbach  65  feet 


aNorton,  W.  H.,  et  al.  Underground  water  resources  of  Iowa:  U.  S.  Geol.  Survey 
Water-Supplj7  Paper  293,  p.  385,  1912. 


(c)  Partial  log  of  Chicago  and  North  Western  Railway  well, 
West  Chicago,  Du  Page  County6 


1285 

Sandstone,  coarse  to  medium  grained,  white .  20  1305 

Sandstone,  coarse  to  fine  grained,  white  and  yellowish  gray, 

dolomitic,  hard .  100  1405 

Sandstone,  medium  to  fine  grained,  white  to  light  gray,  dolomitic  25  1430 

Total  Dresbach  145  feet 


^Samples  examined  by  R.  C.  Lentz,  inspector. 


(d)  Partial  log  of  village  well,  Grays  Lake,  Lake  County 


1200 

Sandstone,  medium  grained,  white  • . .  60  1260 

Sandstone,  fine  grained,  w7hite .  50  1310 

Total  Dresbach  110  feet 


(e)  Partial  log  of  city  well,  Elmhurst,  Du  Page  County 


Sandstone,  medium  to  fine  grained,  gray  to  white,  slightly 

dolomitic  . 

Sandstone,  fine  grained,  pink,  dolomitic . . . 

Sandstone,  medium  to  fine  grained,  yellowish  gray,  dolomitic 
at  top  . 


1270 

60 

1330 

10 

1340 

50 

1390 

Total  Dresbach  120  feet 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


31 


WATER  SUPPLIES 

The  Dresbach  sandstone  is  one  of  the  best-known  water-bearing 
formations  in  northern  Illinois  and  is  drawn  upon  by  a  very  large  num¬ 
ber  of  deep  wells.  It  is  notable  for  its  high  porosity  and  freedom  from 
objectionable  substances  such  as  dolomite,  calcite,  and  pyrite.  Yields 
from  many  of  the  wells  that  penetrate  no  deeper  than  the  Dresbach  are 
more  than  500  gallons  per  minute  although  a  considerable  portion  of  the 
water  is  derived  from  higher  formations.  It  is  probably  conservative 
to  estimate  that  the  Dresbach  alone  will  furnish  at  least  200  gallons  per 
minute  without  an  excessive  draw-down.22  Wells  at  Bensenville  which 
furnish  water  with  only  0.9  pound  of  encrusting  solids  per  1000  gallons 
draw  to  an  undetermined  extent  on  formations  below  the  Dresbach  but 
not  above  it.  Anderson’s23  average  of  57  analyses  from  wells  in  the 
Dresbach  gives  5.2  pounds  per  1000  gallons,  but  these  wells  are  mainly 
uncased  and  draw  to  a  large  but  unknown  extent  on  the  St.  Peter  and 
other  formations.  The  water  from  the  city  well  at  Pawpaw  carries  less 
than  1.5  pounds.24 


EAU  CLAIRE  FORMATION 
DESCRIPTION 

The  Eau  Claire  formation  consists  of  fine-grained,  dolomitic  sand¬ 
stone  of  gray  and  pink  colors,  calcareous  shales  of  red,  gray,  and  green 
colors  called  “marl”  by  drillers,  and  more  or  less  sandy  and  shaly  gray 
to  blue  dolomite.  The  sandstones  are  in  many  places  hard  enough  to 
break  in  chips  and  are  often  logged  as  “lime”.  The  upper  limits  of  the 
formation  may  be  distinguished  by  the  change  from  clean  sandstone  to 
either  shale  or  fine-grained  dolomitic  sandstone.  The  Eau  Claire  is 
noted  for  its  variability  and  scarcely  any  two  wells  show  the  same  suc¬ 
cession  in  detail.  Sandstone  appears  to  be  more  abundant  near  the 
middle  of  the  formation.  The  lower  limit  of  the  Eau  Claire  formation 
is  difficult  to  determine  in  some  logs,  for  there  are  local  layers  of  shale 
as  far  down  as  the  drill  has  penetrated;  in  general  it  should  be  placed 
at  the  bottom  of  the  shale,  dolomite,  and  fine-grained  dolomitic  sand¬ 
stones.  With  this  definition  of  the  upper  and  lower  limits  of  the  forma¬ 
tion,  a  thickness  of  from  300  to  nearly  400  feet  is  obtained.  The  logs  in 
Table  12  illustrate  the  character  of  the  Eau  Claire. 


22The  subject  of  the  relative  draw-down  or  specific  capacity  of  wells  has  not  been 
investigated  as  the  known  data  are  contradictory.  The  writer  believes  that  few  wells  in 
the  Chicago  district  now  furnish  much  more  than  5  gallons  per  minute  per  foot  of  lower¬ 
ing  except  where  some  of  the  water  comes  from  large  opening  or  crevices. 

23Anderson,  C.  B.,  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol. 
Survey  Bull.  34,  p.  99,  1919. 

24Habermeyer,  G.  C.,  Public  ground-water  supplies  in  Illinois:  Illinois  State  Water 
Survey  Bull.  2i,  p.  501,  1925. 


32 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


Table  12. — JV ell  logs  illustrating  character  of  the  Eau  Claire  formation 


(a)  Partial  log  of  city  well,  Galena,  Jo  Daviess  County 

Thickness  Depth 
Feet  Feet 


840 

Sandstone,  medium  to  fine  grained,  gray  glauconitic .  20  860 

Sandstone,  like  above,  with  gray  sandy  shale .  60  920 

Sandstone,  fine  grained,  gray,  dolomitic,  hard,  some  gray  shale 

and  pyrite  .  30  950 

Shale,  gray,  sandy,  dolomitic,  pyritic .  10  960 

Sandstone,  medium  grained,  gray,  pink  and  red,  dolomitic,  glau¬ 
conitic,  with  greenish  gray  dolomitic  shale .  190  1150 

Total  Eau  Claire  310  feet 


(b)  Partial  log  of  Chicago  and  Northwestern  Railway  well, 
West  Chicago,  Du  Page  County® 


Thickness  Depth 
Feet  Feet 


1430 

Sandstone,  coarse  grained,  gray,  with  blue  dolomitic  shale .  25  1455 

Shale,  greenish  blue,  slightly  dolomitic,  sandy .  25  1480 

Shale,  grayish  blue,  dolomitic  . 20  1500 

Sandstone,  coarse  to  very  fine  grained,  light  gray .  15  1515 

Shale,  mixed  gray  and  red,  sandy,  dolomitic .  10  1525 

Sandstone,  medium  to  fine  grained,  gray  to  light  pink,  dolomitic, 

with  gray  dolomitic,  glauconitic  shale .  30  D5^ 

Sandstone,  very  fine  grained,  yellowish  gray  .  10  1565 

Sandstone,  medium  to  fine  grained,  gray  to  light  pink,  with  gray 

dolomitic  glauconitic  shale  .  30  159^ 

Shale,  greenish  blue,  sandy,  pyritic .  10  160^ 

Dolomite,  gray  to  dark  blue,  with  dark  gray  glauconitic  shale.  .  .  .  125  1730 

Dolomite,  white  to  light  gray,  with  dark  gray  dolomitic  and  non- 

dolomitic  shale  layers .  70  1800 

Total  Eau  Claire  370  feet 


ctSamples  examined  by  R.  C.  Lentz,  Inspector. 


(c)  Partial  log  of  well  at  St.  Mary’s  Academy,  Des  Plaines,  Cook 


Shale,  gray,  dolomitic . 

Sandstone,  fine  grained,  gray,  dolomitic . 

Sandstone,  like  above  with  gray  shale . 

No  sample  . .  : . 

Sandstone,  medium  grained,  gray,  very  dolomitic,  glauconitic. 

with  gray  shale  . 

Shale,  gray,  dolomitic  . . . 

Sandstone,  fine  grained,  gray,  dolomitic,  glauconitic,  shaly . . . .  •  • 

Shale,  gray,  dolomitic  . . •  • . 

Sandstone,  very  fine  grained,  gray,  very  dolomitic,  hard . 

Sandstone,  like  above  with  gray  shale . 

No  sample  . 

Shale,  gray,  dolomitic  . •  . . . 

Sandstone,  very  fine  grained,  gray,  very  dolomitic,  with  some 

gray  shale  . .  . . /;••••. . 

Sandstone,  fine  grained,  gray,  dolomitic,  glauconitic,  with  some 

gray  dolomitic  shale  . 


Cook 

County 

1115 

1 

1116 

24 

1140 

5 

1145 

5 

1150 

15 

1165 

10 

1175 

10 

1185 

15 

1200 

35 

1235 

5 

1240 

10 

1250 

1 

1251 

34 

1285 

65 

1350 

STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


33 


(c)  Partial  log  of  well  at  St.  Mary’s  Academy,  Des  Plaines, 

Cook  County  (Concluded) 


Sandstone,  medium  to  very  fine  grained,  gray  and  light  pink, 
very  dolomitic,  some  hard  layers,  some  greenish  gray  dolo- 

mitic  shale,  some  glauconite . 

Sandstone,  very  fine  grained,  gray,  very  dolomitic  and  glauconitic 
Sandstone,  fine  to  medium  grained,  gray  and  pink,  dolomitic, 

hard,  glauconitic  . 

Sandstone,  fine,  gray,  dolomitic,  glauconitic  . . 

Shale,  greenish  gray,  dolomitic,  sandy . 

Sandstone,  fine  to  medium  grained,  gray  and  pink,  dolomitic, 

hard . . . 

Sandstone,  fine  grained,  gray,  dolomitic  . . 

No  sample  . 

Shale,  gray,  dolomitic  . 

Sandstone,  fine  grained,  gray,  dolomitic . 

Total  Eau  Claire  375  feet 


50 

1400 

20 

1420 

5 

1425 

5 

1430 

5 

1435 

15 

1450 

20 

1470 

5 

1475 

10 

1485 

5 

1490 

(d)  Partial  log  of  Ogden  Armour  well,  Lake  Forest,  Lake  County 


Thickness  Depth 
Feet  Feet 


1360 

Sandstone,  fine  grained,  pink,  domolitic;  with  shale,  red,  dolomitic  10  1370 

Sandstone,  fine  grained,  gray,  dolomitic;  with  green  dolomitic 

shale .  30  1400 

Shale,  sandy,  pink  to  gray,  slightly  glauconitic,  dolomitic .  90  1490 

Sandstone,  medium  to  fine  grained,  gray,  dolomitic .  80  1570 

Dolomite,  mainly  very  sandy,  gray;  some  glauconite . 30  1600 

Sandstone,  fine  grained,  gray,  very  dolomitic,  layers  of  greenish 

gray  dolomitic  shale  .  70  1670 

Total  Eau  Claire  310  feet 


WATER  SUPPLIES 

The  wells  in  the  Chicago  and  North  Western  Railway  yards  at 
Proviso  described  by  Anderson25  are  the  only  ones  known  to  the  writer 
which  are  so  cased  that  they  derive  all  of  their  water  from  the  Eau  Claire 
formation.  They  yield  water  with  less  than  one  pound  of  encrusting 
solids  per  1000  gallons  but  at  the  cost  of  the  excessive  draw-down  of 
one  foot  per  gallon  per  minute.  Locomotive  engineers  complain  that 
this  water  foams.  The  foaming  is  apparently  due  to  the  large  content 
of  alkalies.  At  Western  Springs20  water  from  the  Dresbach  and  Eau 
Claire  formations  contains  nearly  6  pounds  of  encrusting  solids  in  1000 
gallons.  It  is  probable  that  the  quality  of  water  in  the  Eau  Claire  varies 
greatly  but,  as  a  whole,  the  formation  yields  little  water.  LTnless  it  is 
desired  to  reach  the  underlying  Mt.  Simon  sandstone  it  is  inadvisable 
to  drill  into  the  Eau  Claire  farther  than  to  form  a  settling  basin  for 
caved  material  from  the  overlying  formations  in  the  well.  -  * 

.  , _  1  i  f  >  j 

/  ' 

25Anderson,  C.  B.,  The  artesian  waters  of  northeastern  Illinois;  Illinois  State  Geol. 
Survey  Bull.  34,  pp.  116-120,  236,  297-298,  1919. 

26Habermeyer,  O.  C.,  Public  ground-water  supplies  in  Illinois:  Illinois  State  Water 
Survey  Bull.  2i,  p.  682,  1925. 


34 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


DRILLING  CONDITIONS 

The  writer  has  not  learned  of  any  particular  difficulties  that  are  met 
in  drilling-  through  the  Eau  Claire  formation.  The  shales  are  firm 
enough  in  most  localities  to  be  left  uncased.  Some  of  the  more  dolomitic 
rocks  drill  very  slowly. 

MT.  SIMON  SANDSTONE 
DESCRIPTION 

The  Mt.  Simon  sandstone  is  fine-  to  very  coarse-grained;  its  finer 
portions  are  mostly  gray  and  some  of  the  coarser  beds  are  pink  or  red. 
It  is  probable  that  the  amount  of  coarse  red  sandstone  increases  with 
depth  below  the  top  of  the  formation  as  is  indicated  by  the  logs  in  Table 
13.  There  are  some  thin  layers  of  red  and  gray  non-dolomitic  shale 
which  appear  to  be  erratic  in  distribution.  The  Mt.  Simon  sandstone 
has  never  been  completely  penetrated  in  Illinois;  the  farthest  that  it 
has  been  entered,  so  far  as  the  writer  has  been  able  to  learn,  is  842  feet 
at  Dixon. 

Table  13. — JV ell  logs  illustrating  character  of  the  Mt.  Simon  sandstone 


(a)  Partial  log  of  Chicago  and  North  Western  Railway  well, 

West  Chicago,  Du  Page  Countya 

Thickness  Depth 
Feet  Feet 


1800 

Sandstone,  medium  grained,  white  to  light  gray,  pyritic .  10  1810 

Sandstone,  medium  to  fine  grained,  white  to  light  gray  and  pink; 

dolomitic  in  part  .  15  1825 

Sandstone,  coarse  to  fine  grained,  white  to  light  gray,  some  pink  10  1835 

Sandstone,  coarse  to  very  fine  grained,  white  to  light  gray 15  1850 

Sandstone,  coarse  to  very  fine  grained,  gray  to  yellowish  gray, 

some  pink  layers  .  30  1880 

Sandstone,  coarse  to  very  fine  grained,  pink . •  • . .  30  1910 

Sandstone,  coarse  to  very  fine  grained,  gray  to  yellowish  gray; 

with  some  pink  layers  .  60  1970 

Sandstone,  coarse  to  very  fine  grained,  light  pink...... .  50  2020 

Sandstone,  coarse  to  very  fine  grained,  gray,  yellow,  and  pink..  62  2082 

Mt.  Simon  penetrated  282  feet.  


aSamples  examined  by  R.  C.  Lentz,  inspector. 


(b)  Partial  log  of  city  well  No.  8,  Rockford,  Winnebago  County 


Sandstone,  fine  to  medium  grained,  white . 

Sandstone,  fine  to  medium  grained,  gray,  shaly . 

Sandstone,  fine  to  medium  grained,  white . 

Sandstone,  fine  to  very  coarse  grained,  gray . 

Sandstone,  fine  to  medium  grained,  gray . 

Sandstone,  fine  to  very  coarse  grained,  gray . 

Sandstone,  very  fine  grained,  gray . 

Sandstone,  fine  to  very  coarse  grained,  gray . 

Sandstone,  fine  to  very  coarse  grained,  pink . 

Sandstone,  fine  to  very  coarse  grained,  gray . 

Sandstone,  fine  to  very  coarse  grained,  pink . 

Sandstone,  very  fine  to  fine  grained  gray  and  yellow.... . 

Sandstone,  very  fine  grained,  dark  pink . • . ... 

Sandstone,  fine  to  very  coarse  grained,  angular  grains,  dark  pink 
Mt.  Simon  penetrated  710  feet _ 


280 

790 

1070 

20 

1090 

30 

1120 

35 

1155 

5 

1160 

10 

1170 

20 

1190 

70 

1260 

10 

1270 

20 

1290 

10 

1300 

20 

1320 

90 

1410 

90 

1500 

STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


35 


(c)  Partial  log  of  wells  at  Dixon  Epileptic  Colony,  near  Dixon,  Lee  County^ 


Sandstone  medium  grained,  white,  some  glauconite  and  pyrite.. 

Sandstone,  coarse  grained,  white,  some  pyrite . 

Sandstone,  coarse  to  medium  grained,  gray,  pyritic . 

Sandstone,  medium  to  very  coarse  grained,  white  and  gray . 

Sandstone,  fine  to  very  coarse  grained,  yellow  to  reddish  brown 

Sandstone,  fine  to  medium  grained,  white  -  - . . 

Sandstone,  fine  to  medium  grained,  light  pink  and  brownish 

yellow  . 

Sandstone,  medium  to  coarse  grained,  pink . 

Sandstone,  coarse  to  exceedingly  coarse  grained,  brownish  red, 

yellow,  pink,  gray,  subangular  grains . 

Sandstone  and  shale,  dark  red . 

Sandstone,  coarse  to  medium,  pink  . 

Sandstone,  medium  to  fine  grained,  dark  red . 

Sandstone,  very  coarse  grained,  red  . 

Sandstone,  coarse  to  medium  grained,  pink . 


140 

1080 

1220 

50 

1270 

50 

1320 

30 

1350 

230 

1580 

44 

1624 

38 

1662 

42 

1704 

76 

1780 

3 

1783 

42 

1825 

38 

1863 

8 

1871 

51 

1922 

Mt.  Simon  penetrated  842  feet 


^Samples  described  by  C.  B.  Anderson  and  T.  E.  Savage. 

WATER  SUPPLIES 

The  coarse  layers  of  the  Mt.  Simon  sandstone  furnish  large  quanti¬ 
ties  of  water,  sufficient  in  some  localities  to  mask  the  character  of  the 
waters  from  higher  formations.  The  very  coarse  layers  are  erratic  in 
distribution  and  are  interbedded  with  fine-grained  sandstones  which  sup¬ 
ply  little  water.  It  follows  that  adjacent  wells  may  find  different  con¬ 
ditions  even  at  the  same  stratigraphic  level.  As  the  Mt.  Simon  is  drawn 
upon  by  fewer  wells  than  are  the  higher  formations,  the  level  of  the 
water  in  it  has  not  yet  been  lowered  to  as  great  an  extent.  Allowance 
must  be  made  for  the  fact  that  the  diameter  of  many  old  wells  was  so 
small  that  they  either  supply  little  water  from  the  deeper  formations  or 
have  long  since  caved  or  “bridged”  at  higher  levels.  For  instance,  it  was 
noted  that  the  old  well  of  the  Chicago  and  North  Western  Railway  at 
West  Chicago  did  not  interfere  with  the  new  well  about  25  feet  away 
after  the  St.  Peter  had  been  cased  off  in  the  latter;  this  lack  of  inter¬ 
ference  demonstrated  that  the  old  well  had  caved  below  the  St.  Peter. 
The  waters  of  the  Mt.  Simon  are  in  general  more  highly  mineralized  than 
are  those  from  higher  formations27  if  total  solids  alone  are  considered, 
but  for  the  most  part  they  contain  less  encrusting  solids  than  do  the 
shallower  waters.  The  water  from  the  Mt.  Simon  at  Western  Springs 
contains  about  3  pounds  of  encrusting  solids  per  1000  gallons.  Less 
than  2  pounds  in  the  same  quantity  is  reported  at  Galena. 2S  The  depth 


27Anderson,  C.  B.,  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol. 
Survey  Bull.  34,  p.  102,  1919. 

28Habermeyer,  G.  C.,  Public  ground-water  supplies  in  Illinois:  Illinois  State  Water 
Survey  Bull.  21,  pp.  239,  683,  1925. 


36 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE,  OF  NORTHERN  ILLINOIS 


at  which  salt  water  appears  varies  greatly  from  place  to  place  but  the 
fact  has  been  given  comparatively  little  attention  as  wells  are  now 
rarely  drilled  deep  enough  to  strike  such  water.  It  appears  probable 
that  this  condition  is  due  to  the  lenticular  character  of  the  coarse  layers 
so  that  flushing  has  extended  to  different  depths  in  various  places.  The 
presence  of  wells  that  have  artificially  accelerated  the  circulation  is  also 
important.  As  a  general  rule  salt  water  is  to  be  feared  in  the  Chicago 
district  at  any  depth  greater  than  2000  feet  although  there  are  several 
successful  wells  of  greater  depths.  Contrary  to  popular  ideas  the  con¬ 
tact  between  fresh  and  salt  waters  is  relatively  abrupt.  The  best  way 
to  guard  against  drilling  into  salt  water  is  to  take  samples  of  water  from 
the  bottom  of  the  hole  with  either  the  bailer  or  the  sand-pump.  If  a  sam¬ 
ple  runs  more  than  150  parts  per  million  of  chlorine,  the  well  should  be 
stopped.  If  the  water  on  pumping  is  too  high  in  salt,  then  a  filling  of 
cement  should  be  placed  to  a  level  above  the  salt-water  stratum. 

DRILLING  CONDITIONS 

Except  for  local  caving  layers  no  particular  drilling  difficulties  in 
the  Mt.  Simon  sandstone  have  come  to  the  attention  of  the  writer. 

STRUCTURE 

Introduction 

Although  generally  thought  of  as  horizontal,  the  strata  of  northern 
Illinois  are  inclined  at  angles  which  range  from  a  few  minutes  to  50 
degrees.  Steep  dips  are  found  in:  (1)  the  monoclinal  fold  which  passes 
west  of  Streator  through  La  Salle  and  flattens  out  toward  the  northwest 
(the  west  limb  of  the  La  Salle  anticline)  ;  (2)  the  vicinity  of  Oregon ; 
and  (3)  a  small  district  near  Des  Plaines.  The  La  Salle  anticline  itself, 
distinguished  from  its  western  slope,  is  the  southward  continuation  of 
the  broad  Wisconsin  arch.  On  it  there  are  several  small  domes  and 
its  flanks  are  crenulated  with  minor  synclines  and  anticlines  whose  axes 
lie  approximately  east  and  west. 

The  position  of  the  different  rock  formations  in  an  area  of  compara¬ 
tively  gentle  dips  is  best  shown  by  contours  drawn  on  top  of  a  certain 
easily  identified  formation.  These  contours  represent  what  would  be 
the  surface  of  the  land  if  all  overlying  formations  of  rock  and  soil  were 
stripped  off.  Except  as  it  controls  the  position  of  the  outcrops  of  rock 
formations  which  are  resistant  to  weathering  and  erosion,  the  structure 
is  independent  of  the  present  configuration  of  the  surface.  In  Illinois 
much  of  the  present  topography  is  the  result  of  deposition  of  loose 
material  by  glaciers  and  not  of  the  wearing  away  of  the  bed  rocks ;  the 
northwestern  part  of  the  State,  however,  was  not  glaciated.  It  is  diffi¬ 
cult  for  persons  not  experienced  in  geology  to  grasp  the  idea  that  (a)  the 
same  rock  formation  is  not  found  at  the  same  depth  at  all  places,  and 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


37 


(b)  undulations  in  the  bed  rock  formations  are  not  necessarily,  or  indeed 
commonly,  reflected  in  the  shape  of  hills  and  valleys.  Plate  I  was  con¬ 
structed  on  the  basis  of  elevations  of  the  top  of  the  Dresbach  sandstone 
obtained  from  the  wells  tabulated  in  Table  14.  As  the  number  of  wells 
is  insufficient  to  permit  accurate  location  of  the  contours,  a  study  of  the 
interval  between  the  top  of  the  St.  Peter  and  the  top  of  the  Dresbach 
was  made.  This  varies  from  less  than  300  feet  to  nearly  1000  feet;  the 
increase  is  from  northeast  to  southwest  with  only  a  few  minor  irregu¬ 
larities  some  of  which  may  be  due  to  erroneous  well  logs.  The  greatest 
uncertainty  in  the  determination  of  this  interval  is  in  the  western  and 
southern  parts  of  the  map.  With  this  interval  as  a  basis,  the  observed 
elevations  were  supplemented  by  records  of  wells  that  go  no  deeper 
than  the  St.  Peter  and  by  the  structure  map  prepared  by  Cady29  to  show 
the  top  of  the  formation.  If  more  records  of  shallow  wells  in  northern 
Illinois  were  available  the  map  would  be  more  satisfactory  but  this 
region  has  not  been  studied  in  recent  years. 

Plate  II  is  a  section  along  the  line  of  the  Chicago  and  North  West¬ 
ern  Railway  from  Clinton,  Iowa,  to  Chicago.  The  vertical  scale  is  ex¬ 
aggerated  about  70  times  so  that  the  inclination  of  the  rock  is  shown 
at  much  too  great  an  angle  in  order  to  make  the  scale  of  the  well  logs 
large  enough  to  give  the  necessary  information.  Lines  between  wells 
simply  connect  similar  formations  and  do  not  necessarily  indicate  the 
variations  in  the  formations  between  the  points  of  observation.  No  at¬ 
tempt  has  been  made  to  show  the  surface  either  of  the  ground  or  of  the 
bed  rock. 

Structual  Features 

Attention  has  already  been  called  to  the  La  Salle  anticline  which 
separates  the  northeastern  region  of  relatively  elevated  strata  from  the 
deep  basin  to  the  southwest.  On  account  of  the  increase  in  the  St.  Peter- 
Dresbach  interval  toward  the  southwest,  this  basin  is  much  deeper  than 
that  in  the  top  of  the  St.  Peter.  Little  is  known  of  the  forms  in  the 
deeper  strata  of  the  comparatively  abrupt  domes  of  the  region  near 
Dixon  and  Oregon.  Just  north  of  these,  along  the  Stephenson-Ogle 
county  line,  is  a  marked  syncline  which  extends  entirely  across  the  State. 
Its  exact  shape  is  not  known  in  the  western  part  of  the  area  and  there 
may  be  no  such  enclosed  basin  as  is  shown  around  Freeport.  The  ab¬ 
normal  course  of  Pecatonica  River  is  probably  related  in  part  to  this 
flexure.  The  syncline  is  best  developed  in  McHenry  and  Lake  counties. 

South  of  this  syncline  is  an  anticline  which  can  be  traced  from  the 
vicinity  of  Savannah,  Carroll  County,  east  through  the  domes  at  For- 
reston  and  Leaf  River,  Ogle  County,  to  just  north  of  Des  Plaines,  Cook 

29Cady,  G.  IT.,  Structure  of  the  Ua  Salle  anticline:  Illinois  State  Geol.  Survey  Buil 
36,  pp.  85-179,  1920. 


Table  14. —  Well  data  used  in  the  construction  of  the  structure  map  (PI.  I) 


38 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


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STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


County,  and  which  is  an  extension  of  Cady’s  “Savanna-Sabula  anticline”. 
At  Des  Plaines  the  south  limb  of  this  fold  is  apparently  marked  by  a 
fault  which  farther  east  seems  to  pass  into  a  monocline  and  to  the  south 
of  which  is  a  small  basin.  The  evidence  of  faulting-  is  the  broken  con¬ 
dition  of  the  rocks  in  the  Des  Plaines  city  well,  determined  both  by  ex¬ 
amination  of  the  samples  and  from  information  given  by  the  driller. 
Great  difficulty  was  experienced  in  drilling  this  well  and  after  several 
liners  were  side-tracked  the  Avell  was  cased  to  the  bottom  at  1600 
feet.  The  cuttings  from  the  sandstones  were  muddy  and  little  water 
could  be  obtained.  In  addition,  the  Prairie  du  Chien  dolomite  appears 
to  be  absent  so  that  the  evidence  favors  the  view  that  this  well  passed 
through  a  south-dipping  normal  fault.  About  a  mile  and  a  half  to  the 
east  the  well  at  the  Crotian  Orphanage  encountered  somewhat  similar 
conditions  and  very  little  water  was  found  at  any  depth.  A  well  at  the 
city  hall  was  reported  as  finding  “shale”  to  a  depth  of  1800  feet.30  Where 
cuttings  have  been  examined,  however,  it  has  been  found  that  the  forma¬ 
tions  occur  in  the  usual  order,  although  much  broken,  and  in  the  Orphan¬ 
age  well  with  thicknesses  about  30  per  cent  greater  than  the  normal 
thickness  for  the  vicinity.  The  latter  fact  suggests  that  in  places  the 
fault  passes  into  a  monocline  with  the  strata  dipping  at  a  considerable 
angle.  The  St.  Peter  sandstone  is  500  feet  deeper  at  the  Orphanage  than 
at  St.  Mary's  Academy,  only  a  trifle  more  than  two  miles  to  the  north. 
Whatever  the  true  explanation  of  these  phenomena  may  be,  the  writer 
advises  that  well  drillers  avoid  an  east-west  belt  through  the  southern 
part  of  Des  Plaines  for  several  miles  in  each  direction. 

Farther  south  there  is  a  marked  syncline  in  northern  Kendall 
County  which  strikes  northwest-southeast.  This  is  associated  with  an 
offshoot  of  the  Wisconsin  anticline  which  extends  southeast  from  the 
Oregon  dome  through  the  St.  Peter  outcrops  in  northeastern  La  Salle 
County  to  Kankakee,  and  which  was  named  the  Kankakee  anticline  by 
Cadv.31  Southwest  of  the  Kankakee  anticline  a  syncline  passes  through 
Grundy  County  and  separates  the  anticline  from  the  true  La  Salle  anti¬ 
cline  east  of  La  Salle  and  Streator  which  has  a  more  nearly  north-south 
strike. 

Although  it  cannot  be  expected  that  the  structure  map  will  prove 
to  be  absolutely  accurate  at  all  points,  it  serves  as  a  basis  for  correlating 
and  evaluating  the  known  data  so  that  estimates  of  the  depth  to  the  top 
of  the  Dresbach  sandstone  can  be  made  on  a  definite  and  concrete  basis. 


30Habermeyer,  G.  C.,  Public  ground- water  supplies  in  Illinois:  Illinois  State  Water 
Survey  Bull.  21,  p.  174,  1925. 

3iCady,  G.  H.,  The  structure  of  the  La  Salle  anticline:  Illinois  State  Geol.  Survey 
Bull.  36.  p.  133,  1920. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


43 


The  intervals  shown  serve  as  a  check,  for  when  the  top  of  the  St.  Peter 
is  reached  they  allow  of  an  estimate  of  the  distance  to  the  top  of  the 
Dresbach. 

Cause  of  Deformation 

Judging  from  the  conditions  around  the  partly  exhumed  pre-Cam¬ 
brian  monadnocks  of  Wisconsin  and  modern  theories  of  the  origin  of 
folds  in  the  mid-continent  oil  fields,  the  structural  features  of  northern 
Illinois  are  probably  due  to  irregularities  in  the  pre-Cambrian  basement. 
Cady  concluded  that  the  La  Salle  anticline  ‘‘is  strongly  suggestive  of 
an  initial  line  of  weakness  .  .  .  possibly  due  to  a  concealed  fault  line 

which  may  be  present  in  the  deeply  buried  rocks  .  .  .”32 

WATER  QUALITY  AND  PROBLEMS 
General  Statement 

It  is  impossible  with  present  knowledge  fully  to  discuss  the  quality 
of  the  waters  in  the  several  formations.  It  so  happens  that  a  number  of 
persons  who  have  been  exploring  for  softer  waters  than  those  furnished 
by  ordinary  uncased  wells  are  not  at  present  willing  to  reveal  all  the  in¬ 
formation  that  they  have  collected  at  considerable  expense.  Some  of 
the  methods  of  casing  wells  are  regarded  as  trade  secrets  as  they  are 
not  followed  by  all  well  drillers.  Nevertheless,  some  facts  are  so  well 
known  that  they  can  profitably  be  recapitulated.33 

Nature  of  Soft  Waters 

The  waters  of  northern  Illinois  generally  increase  in  total  solids 
with  depth,  but  the  character  of  the  bases  present  varies  greatly.  Near 
the  surface  alkaline  earths  (calcium  and  magnesium)  predominate  but 
with  depth  alkalies  (sodium  and  potassium)  increase  in  amount.  This  in¬ 
crease  is  for  the  most  part  accompanied  by  larger  amounts  of  chlorides 
and  sulphates.  Very  deep  waters  are  foaming,  corrosive,  and  undrink¬ 
able  but  some  intermediate  waters  contain  only  a  moderate  amount,  less 
than  one  pound  per  1,000  gallons,  of  encrusting  solids.  The  waters  also 
vary  in  amount  of  sulphate  which  when  combined  with  calcium  or  mag¬ 
nesium  makes  the  most  objectionable  form  of  scale  in  boilers.  The 
mineral  character  of  the  waters  is  also  related  to  the  kinds  of  rocks  from 
which  they  come  and  in  general  the  best  water  comes  from  pure  quartz 
sandstones.  The  cause  of  the  decrease  in  alkaline  earths  with  depth  is 
not  as  yet  definitely  known.  It  is  quite  possible  that  the  work  of  Renick34 

32lclem,  p.  179. 

33Anderson,  C.  B.,  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol. 
Survey  Bull.  34,  pp.  100-101,  116-120,  140,  142,  236;  297-298,  300,  1919. 

Habermeyer,  G.  C.,  Public  ground-water  supplies  in  Illinois:  Ilinois  State  Water 
Survey  Bull.  21,  1925. 

34Renick,  B.  C.,  Base  exchange,  in  ground  water  by  silicates  as  illustrated  in  Montana: 
IJ.  S.  Geol.  Survey  Water-Supply  Paper  520.  pp.  53-72,  1924. 


44 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


in  Montana  may  prove  to  explain  the  phenomenon  as  one  analogous  to 
that  alteration  which  takes  place  in  a  zeolite  water-softener. 

Methods  of  Testing  Quality  of  Water 

The  ideal  method  of  testing  the  quality  of  the  water  from  different 
formations  is  to  set  casing  down  to  the  top  of  the  stratum  and  then  make 
a  pumping  test.  The  expense  of  such  a  procedure  generally  prohibits 
following  it  so  that  it  is  customary  to  take  samples  of  water  with  a  bailer 
or  sand-pump.  Some  of  the  results  thus  obtained  do  not  show  the  true 
character  of  the  water  in  the  formation  which  the  bottom  of  the  well  has 
reached  when  the  sample  is  taken.  The  principal  causes  of  such  fail¬ 
ure  are :  (a)  The  head  of  water  is  greater  in  the  shallow  formations  than 
in  the  deep  ones  so  that  surface  waters  run  down  the  well  and  force 
away  the  deep-seated  waters,  (b)  The  valve  in  the  bottom  of  the  bailer 
leaks,  (c)  The  bailer  is  short  and  allows  the  mixture  of  waters  at  the 
top  while  hoisting,  (d)  The  waters  diffuse  as  a  result  of  drilling  opera¬ 
tions  or  of  a  long  wait  after  drilling  which  allows  circulation  due  to 
thermal  differences.  The  writer  has  noted  diffusion  of  waters  when 
taking  temperatures  in  a  12-inch  hole.  The  sand-pump  is  preferable  to 
the  baler  in  that  its  top  is  closed  although  there  is  danger  that  a  change 
in  rate  of  lowering  may  cause  it  to  open  before  the  bottom  of  the  run  is 
reached.  Experience  has  shown  that  tests  of  water  obtained  in  this 
manner  are  reasonably  reliable  only  when  the  water  lever  is  constantly 
rising  as  the  well  is  drilled  deeper.  Then  they  are  checked  by  pumping 
tests  within  a  reasonable  margin  of  error.  Such  tests  are  worthless 
(a)  when  the  water  level  falls  as  the  well  is  deepened  and  (b)  when  the 
lower  formations  carry  little  water.  In  judging  of  the  quality  of  water 
which  will  be  obtained  on  completion  of  the  well  it  must  be  realized 
that  (a)  bailer  tests  show  nothing  as  to  the  yield  of  the  different  forma¬ 
tions,  and  (b)  many  wells  yield  better  water  after  prolonged  pumping 
as  a  result  of  the  artificial  acceleration  of  the  flow  of  water  which  washes 
out  the  more  soluble  substances. 

The  following  deep  wells  are  reported  as  yielding  water  with  less 
than  two  pounds  of  encrusting  solids  per  1,000  gallons: 

Chicago,  Milwaukee  and  St.  Paul  Ry.,  Bensenville. 

Chicago  and  North  Western  Ry.,  Proviso  and  West  Chicago. 

St.  Mary’s  Seminary,  Area  (Mundelein). 

St.  Mary’s  Academy,  Des  Plaines. 

Ogden  Armour,  Lake  Forest. 

Abott  Laboratories,  North  Chicago. 

Waterworks,  Batavia,  Bensenville,  Hanover,  Morrison,  Pawpaw,  Riverside, 
St.  Charles.35 

The  Bensenville  railroad  wells  are  cased  to  the  Dresbach,  and  the 
Proviso  wells  to  the  Eau  Claire;  the  others  either  have  a  confidential 

3oHabermeyer,  G.  C.,  Public  ground-water  supplies  in  Illinois:  Illinois  State  Water 
Survey  Bull.  2i,  pp.  57,  274,  436,  501,  551,  582,  1925. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


45 


casing  log  or  obtain  so  much  water  from  low  formations  that  the  lack  of 
casing  is  not  apparent.  The  yields  from  some  of  these  wells  is  as  much 
as  600  to  800  gallons  per  minute.  It  must  be  realized  that  the  construc¬ 
tion  of  a  soft  water  well  near  an  uncased  well  is  nearly  impossible  be¬ 
cause  waters  from  several  formations  may  pass  through  the  latter  and 
thus  reach  the  cased  well. 

Contamination  of  Deep  Wells 

Flowing  wells  are  safe,  even  if  not  cased  through  contaminated 
upper  formations,  as  above  the  artesian  stratum  the  flow  of  water  is  out¬ 
ward  from  the  well.  In  the  Chicago  district  the  deeper  waters  now  have 
a  head  far  below  that  of  the  shallow  waters.  In  such  circumstances 
casing  with  a  good  shut-off  at  the  bottom  is  essential  to  a  safe  water 
supply.  Two  wells  are  known  of  where  very  bad  water  was  obtained 
at  depths  greater  than  1,000  feet.  The  tests  in  each  well  showed  a  good 
shut-off  below  the  Maquoketa  shale,  but  during  drilling  bad  smelling 
water  was  observed  to  come  from  crevices  in  the  Prairie  du  Chein  for¬ 
mation.  It  has  been  suggested  that  sewage  is  being  emptied  into  some 
abandoned  well  which  is  possibly  many  miles  from  the  locations  of  these 
contaminated  wells.  In  one  well  a  packer  set  in  the  Mazomanie  sand¬ 
stone  removed  the  trouble,  but  no  information  has  been  received  as  to 
the  other  well  although  it  has  been  worked  on  for  several  years. 

Well  Construction 

No  exhaustive  discussion  of  methods  of  well  construction  can  be 
attempted  here.36  Engineers  are  urged  to  devote  careful  attention  to 
the  quality  of  the  casing  and  to  the  shut-off  at  the  bottom  of  each  string 
of  pipe.  It  is  not  enough  simply  to  drop  pipe  into  a  hole  either  with 
or  without  casing  shoe.  The  character  of  the  rock  in  which  the  shoulder 
is  made  must  be  considered,  and  brittle,  fractured  formations  avoided. 
Large  crevices  are  most  common  near  abrupt  changes  in  the  character 
of  the  rock.  It  must  be  realized  that  holes  of  different  sizes  are  rarely 
concentric  and  that  lead  seals  between  different  sizes  of  pipe  make 
joints  of  indifferent  quality.  It  is  far  better  to  follow  oil  well  practice 
and  have  the  last  string  of  pipe  extend  to  the  surface.  Shut-offs  in  water 
wells  may  be  tested  by  (a)  placing  a  dye  (fluorescein)  in  the  water 

3fiMore  information  on  well  drilling  methods  can  be  obtained  from: 

Bowman,  Isaiah,  Well-drilling  methods:  U.  S.  Geol.  Survey  Water-Supply  Paper 
257,  1911. 

Day,  JD.  H..  Handbook  of  the  petroleum  industry,  New  York,  1922. 

Jeffry,  W.  H.,  Deep  well  drilling,  Toledo,  1921. 

Sanderson,  R.  R  ,  Drill  work,  methods  and  costs,  Cyclone  Drill  Co.,  1911. 

Thompson,  A.  B.,  Oil  field  development,  pp.  307-409,  New  York,  1916 

Uren,  L.  C.,  Textbook  of  petroleum  production  engineering,  pp.  89-143,  201-301,  New 
York,  1924. 

Woodworth,  R.  B.,  The  evolution  of  drilling  rigs:  Amer.  Inst.  Min.  Eng.  Trans.,  vol. 
54,  pp.  210-268,  1915. 

Ziegler,  Victor,  Oil  well  drilling  methods,  New  York,  1923. 


46 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


between  the  different  strings  of  pipe,  and  (b)  observing  the  water  levels 
inside  and  outside  a  string  of  pipe  when  the  level  is  changed  in  the 
inner  pipe  by  pumping  or  bailing.  An  excellent  shut-off  may  be  made 
by  cementing  the  bottom  of  each  string  of  pipe.  This  is  best  done  before 
the  hole  is  drilled  any  deeper  but  many  drillers  prefer  to  leave  casing 
until  all  drilling  has  been  completed  for  fear  that  in  a  crooked  hole  the 
wire  line  will  wear  through  the  pipe.  It  is  advisable  to  use  cement  thick 
enough  to  protect  the  well  from  contaminated  waters  even  without  any 
pipe ;  this  should  extend  from  the  surface  through  all  contaminated 
waters.  At  lower  levels  many  prefer  clay  instead  of  cement  since  that 
does  not  prevent  the  withdrawal  of  rusted  pipe.  Cementing  of  well 
casing  is  now  standard  practice  in  oil  wells  and  its  adoption  in  water 
wells  is  worth  careful  consideration.37  Although  the  use  of  “genuine 
wrought  iron”  pipe  is  far  preferable  to  that  of  the  mild  steel  known  to 
the  trade  as  “wrought  iron,”  it  is  well  to  remember  that  the  best  pipe 
will  rust  out  in  time  since  the  waters  from  great  depths,  with  the  relief 
of  pressure  on  being  brought  to  the  surface,  evolve  much  carbon 
dioxide.  In  wells  pumped  directly  into  the  mains  this  evolution  of  gas 
often  causes  foamy  water  as  well  as  the  precipitation  of  calcium  carbon¬ 
ate.  Where  the  air  lift  is  employed,  these  processes  take  place  in  the 
tank  and  some  of  the  dissolved  iron  is  also  oxidized  and  settles  out.  The 
freeing  of  gas  is  more  pronounced  in  wells  which  are  cased  to  great 
depths  since  all  of  the  water  comes  from  formations  where  the  gas  was 
under  high  pressure.  Some  cases  of  precipitation  may  be  due  to  mingling 
of  waters  from  different  formations.  Engineers  should  remember  that 
although  the  methods  employed  in  well  drilling  and  construction  appear 
very  simple,  their  practical  application  finds  every  well  a  different  en¬ 
gineering  problem.  Although  the  geological  formations  may  be  the 
same,  the  number  and  position  of  fractures,  and  variations  in  hardness 
and  in  porosity  call  for  different  procedure.  In  judging  costs  it  should 
be  realized  that  drilling  in  holes  full  of  water  is  necessarily  much  slower 
than  in  oil  wells,  where  water  is  excluded  as  far  as  possible,  because 
the  friction  on  the  cable  and  tools  lessens  the  force  of  the  blows.  Another 
point  is  that  the  efficiency  of  drilling  depends  to  a  great  extent  on  the 
quality  of  the  tool  dressing;  a  poor  tool  dresser  can  slow  down  the  work 
to  a  remarkable  extent.  A  rule  of  primary  importance  is  that  the  hole 
should  be  kept  large  enough  to  allow  for  unforeseen  caves  which  entail 
reduction  after  the  insertion  of  liners.  Many  engineers  insist  on  butted 
joints  in  drive  pipe,  but  most  drillers  prefer  ordinary  joints  which  may 
be  tightened  from  time  to  time  by  screwing  up  the  pipe.  It  is  said  that 

37Tough,  F.  B.,  Methods  of  shutting  off  water  in  oil  and  gas  wells:  U.  S.  Bur.  Mines 

^  jj  ^.63  1918 

U  Kirchoff'er,  W.  G.,  Grouting  wells  in  rock  formation  effective  and  simple:  Engr. 
News-Record,  vol.  81,  p.  367,  1918. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


47 


if  drilling  is  properly  done,  very  hard  driving  that  might  injure  the 
threads  can  be  avoided.  Liners  in  the  rock  should  not  be  driven  ;  the 
need  to  drive  them  indicates  a  crooked  hole.  Attention  should  be  drawn 
to  the  fact  that  crooked  holes  are  more  common  in  large  than  in  small 
diameters  since  in  the  former  there  is  more  room  for  the  drill  stem  and 
jars  to  swing  to  one  side  of  the  hole.  As  a  general  thing  engineers 
should  be  slow  to  criticise  the  methods  of  experienced  drillers  for  such 
methods  are  the  result  of  years  of  practice  rather  than  of  theory.  Well 
drilling  is  an  art  that  demands  experience  and  ingenuity ;  it  is  an  opera¬ 
tion  in  which,  many  times,  the  personal  factor  is  more  important  than 
the  quality  of  the  machinery.  The  lowest  bidder  is  often  the  most  ex¬ 
pensive  in  the  long  run. 

Future  of  Underground  Waters 

Many  wells  have  been  abandoned  in  Illinois  and  elsewhere  because 
it  was  assumed  that  the  supply  of  water  had  been  exhausted.  Study  of 
old  wells  shows  definitely  that  for  the  most  part  they  were  of  such  small 
diameter  that  they  soon  bridged  or  filled  with  cavings.  In  some  com¬ 
munities,  when  more  water  was  required  new  wells  were  drilled  so  close 
to  the  older  ones  that  the  available  supply  was  simply  divided.  It  is 
absolutely  essential  that  wells  be  spaced  over  considerable  areas.  In 
Chicago  the  water  levels  have  been  greatly  lowered  as  has  been  shown 
by  Anderson.38  The  condition  appears  to  be  local,  although  it  was 
noted  that  at  West  Chicago,  30  miles  away,  the  water  in  the  Dresbach 
is  now  lower  than  the  level  of  Lake  Michigan.  The  reduction  in  water 
pressure  has  probably  resulted  in  settling  and  compacting  of  the  sand¬ 
stones  so  that  the  porosity  of  the  rocks  has  been  permanently  lessened. 
The  situation  in  the  Stock  Yards  district  is  serious  and  from  the  stand¬ 
point  of  conservation  it  seems  a  pity  that  such  vast  quantities  of  pure 
water  are  used  for  washing,  cooling,  boilers,  and  other  industrial  pur¬ 
poses  for  which  lake  water  would  serve  as  well.  It  is  probable  that  in 
smaller  cities  sufficient  water  for  a  public  supply  will  always  be  avail- 
abe.  To  this  end  the  use  of  underground  waters  for  industries  that 
do  not  require  pure  water  should  be  discouraged  in  the  future,  at  least 
where  surface  waters  are  obtainable  at  reasonable  cost. 

Before  concluding  that  public  supplies  from  wells  must  be  aban¬ 
doned,  engineers  should  look  to  see  if  the  shortage  cannot  be  relieved 
by  repair  of  the  wells.  Methods  of  increasing  the  supply  from  old  wells 
comprise  recasing,  cleaning,  reaming,  shooting,  and  deepening.  Many 
drillers  state  that  reaming  is  in  most  cases  more  expensive  than  a  new 
well  and  that  shooting,  although  an  undoubted  benefit  if  crevices  are 
opened  in  the  more  brittle  rocks,  often  causes  permanent  caving  condi- 

38Anderson,  C.  B.,  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol. 
Survey  Bull.  34,  pp.  93-95,  1919. 


48 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


tions  which  soon  offset  the  increase  of  yield.  The  writer  therfore  hesi¬ 
tates  to  recommend  shooting-  as  a  certain  means  of  increasing  well 
yields.39 


Well  Logs 

The  writer  wishes  to  emphasize  the  desirability  of  obtaining  accu¬ 
rate  well  logs  based  both  on  drillers’  records  and  on  the  study  of  cut¬ 
tings  from  every  5-foot  screw.  Bags  for  the  collection  of  samples  are 
furnished  free  by  the  State  Geological  Survey  at  Urbana.  Records  based 
on  examination  of  samples  by  an  experienced  geologist  furnish  much 
more  detailed  data  than  can  be  obtained  from  the  drillers’  log  alone,  but 
the  latter  should  not  be  neglected,  for  in  many  cases  the  action  of  the 
tools  may  tell  as  much  concerning  the  underground  conditions  as  do 
the  samples.  It  is  a  common  fallacy  among  both  geologists  and  en¬ 
gineers  to  think  that  samples  from  churn  drill  holes  are  worthless  on 
account  of  caving.  Such  is  not  the  case,  for  if  caving  equaled  the 
amount  of  new  hole  little  progress  would  be  possible.  Although  it  is 
true  that  caved  material  is  sometimes  troublesome  in  the  study  of  cut¬ 
tings,  it  can  generally  be  distinguished  by  the  large  size  and  unworn 
character  of  the  fragments  and  its  presence  can  always  be  noted  by  an 
experienced  driller.  The  principal  source  of  error  is  the  tendency  of 
drillers  to  take  samples  from  the  slush  pit  when  going  off  shift  instead 
of  direct  from  the  bailer. 

Records  should  include  a  casing  log  which  shows  the  length  and 
position  of  each  string  of  pipe  as  well  as  the  sizes  of  pipe  and  of  hole. 
Whenever  repair  work  or  new  wells  are  needed  such  detailed  records  are 
of  immense  value.  Attention  should  also  be  given  to  the  fact  that  study 
of  underground  temperatures  is  a  guide  to  the  relative  amounts  of  water 
from  different  producing  formations.  Many  temperatures  of  waters 
were  collected  by  Anderson  and  Habermeyer40  which,  when  compared 
with  those  observed  by  R.  C.  Lentz41  at  West  Chicago,  seem  to  indicate 
that  much  water  is  derived  by  uncased  wells  from  the  formations  above 
the  Dresbach  sandstone. 

The  State  Water  Survey  Division  has  many  records  of  well  yields 
and  analyses  of  water  samples  which  are  available  to  persons  who  con¬ 
template  installing  wells.  For  municipalities,  mineral  analysis  of  waters 
will  be  made  free  of  charge  and  assistance  will  be  given  during  tests  of 
yields  whenever  possible. 

SfNorton,  W.  LI.,  Underground  ■water  resources  of  Iowa:  U.  S.  Geol.  Survey  Water- 
Supply  Paper,  293,  p.  131,  1912. 

Kirchoffer,  W.  G.,  Increasing  the  capacity  of  ground  water  supplies:  Amer,  Water 
Works  Assoc.  Jour.,  vol.  15,  pp.  144-151,  1926. 

40Anderson,  C.  EL,  The  artesian  waters  of  northeastern  Illinois:  Illinois  State  Geol. 
Survey  Bull.  34,  pp.  42-50,  1919. 

Habermeyer,  G.  C.,  Public  ground-water  supplies  in  Illinois:  Illinois  State  Water 
Survey  Bull.  21,  1925. 

43 Temperature  at  1650  62°  F.,  at  20S2  75°  F.  Temperature  in  well  at  Madison,  Wis., 
at  840  55°  F. 


STRATIGRAPHY  AND  GEOLOGIC  STRUCTURE  OF  NORTHERN  ILLINOIS 


49 


In  conclusion  the  writer  wishes  to  urge  that  engineers  and  well 
owners  cooperate  with  the  State  Geological  Survey  and  the  State  Water 
Survey  in  collecting  accurate  data  regarding  underground  waters.  There 
can  be  little  serious  question  but  that  a  properly  constructed  well  is  a 
nearly  fool-proof  source  of  pure  water  with  which  no  man-made  filter 
can  compare  in  efficiency  and  safety. 


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